diff --git a/ChangeLog b/ChangeLog
index 44719245..394834ea 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -34,6 +34,9 @@
 - vips_region_shrink() knows about alpha, helps dzsave and tiffsave
 - use expat, not libxml, for XML load ... removes a required dependency, since
   we get expat as part of glib
+- the C functions vips_math2_const(), vips_boolean_const() and 
+  vips_relational_const() have changed argument order to match
+  Python/CLI/C++ ... sorry
 
 8/12/16 started 8.4.5
 - allow libgsf-1.14.26 to help centos, thanks tdiprima
diff --git a/libvips/arithmetic/boolean.c b/libvips/arithmetic/boolean.c
index 2ed8594e..80e2272c 100644
--- a/libvips/arithmetic/boolean.c
+++ b/libvips/arithmetic/boolean.c
@@ -533,7 +533,7 @@ vips_boolean_const_init( VipsBooleanConst *boolean_const )
 
 static int
 vips_boolean_constv( VipsImage *in, VipsImage **out, 
-	VipsOperationBoolean operation, double *c, int n, va_list ap )
+	double *c, int n, VipsOperationBoolean operation, va_list ap )
 {
 	VipsArea *area_c;
 	double *array; 
@@ -546,7 +546,7 @@ vips_boolean_constv( VipsImage *in, VipsImage **out,
 		array[i] = c[i];
 
 	result = vips_call_split( "boolean_const", ap, 
-		in, out, operation, area_c );
+		in, out, area_c, operation );
 
 	vips_area_unref( area_c );
 
@@ -557,9 +557,9 @@ vips_boolean_constv( VipsImage *in, VipsImage **out,
  * vips_boolean_const:
  * @in: input image
  * @out: output image
- * @boolean: boolean operation to perform
  * @c: array of constants 
  * @n: number of constants in @c
+ * @boolean: boolean operation to perform
  * @...: %NULL-terminated list of optional named arguments
  *
  * Perform various boolean operations on an image against an array of
@@ -580,13 +580,13 @@ vips_boolean_constv( VipsImage *in, VipsImage **out,
  */
 int
 vips_boolean_const( VipsImage *in, VipsImage **out, 
-	VipsOperationBoolean boolean, double *c, int n, ... )
+	double *c, int n, VipsOperationBoolean boolean, ... )
 {
 	va_list ap;
 	int result;
 
-	va_start( ap, n );
-	result = vips_boolean_constv( in, out, boolean, c, n, ap );
+	va_start( ap, boolean );
+	result = vips_boolean_constv( in, out, c, n, boolean, ap );
 	va_end( ap );
 
 	return( result );
@@ -615,7 +615,7 @@ vips_andimage_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_AND, c, n, ap );
+		c, n, VIPS_OPERATION_BOOLEAN_AND, ap );
 	va_end( ap );
 
 	return( result );
@@ -644,7 +644,7 @@ vips_orimage_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_OR, c, n, ap );
+		c, n, VIPS_OPERATION_BOOLEAN_OR, ap );
 	va_end( ap );
 
 	return( result );
@@ -673,7 +673,7 @@ vips_eorimage_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_EOR, c, n, ap );
+		c, n, VIPS_OPERATION_BOOLEAN_EOR, ap );
 	va_end( ap );
 
 	return( result );
@@ -702,7 +702,7 @@ vips_lshift_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_LSHIFT, c, n, ap );
+		c, n, VIPS_OPERATION_BOOLEAN_LSHIFT, ap );
 	va_end( ap );
 
 	return( result );
@@ -731,7 +731,7 @@ vips_rshift_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_RSHIFT, c, n, ap );
+		c, n, VIPS_OPERATION_BOOLEAN_RSHIFT, ap );
 	va_end( ap );
 
 	return( result );
@@ -754,13 +754,13 @@ vips_rshift_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
  */
 int
 vips_boolean_const1( VipsImage *in, VipsImage **out, 
-	VipsOperationBoolean boolean, double c, ... )
+	double c, VipsOperationBoolean boolean, ... )
 {
 	va_list ap;
 	int result;
 
-	va_start( ap, c );
-	result = vips_boolean_constv( in, out, boolean, &c, 1, ap );
+	va_start( ap, boolean );
+	result = vips_boolean_constv( in, out, &c, 1, boolean, ap );
 	va_end( ap );
 
 	return( result );
@@ -788,7 +788,7 @@ vips_andimage_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_AND, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_BOOLEAN_AND, ap );
 	va_end( ap );
 
 	return( result );
@@ -816,7 +816,7 @@ vips_orimage_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_OR, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_BOOLEAN_OR, ap );
 	va_end( ap );
 
 	return( result );
@@ -844,7 +844,7 @@ vips_eorimage_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_EOR, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_BOOLEAN_EOR, ap );
 	va_end( ap );
 
 	return( result );
@@ -872,7 +872,7 @@ vips_lshift_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_LSHIFT, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_BOOLEAN_LSHIFT, ap );
 	va_end( ap );
 
 	return( result );
@@ -900,7 +900,7 @@ vips_rshift_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_boolean_constv( in, out, 
-		VIPS_OPERATION_BOOLEAN_RSHIFT, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_BOOLEAN_RSHIFT, ap );
 	va_end( ap );
 
 	return( result );
diff --git a/libvips/arithmetic/math2.c b/libvips/arithmetic/math2.c
index a79f8235..651e5829 100644
--- a/libvips/arithmetic/math2.c
+++ b/libvips/arithmetic/math2.c
@@ -373,11 +373,17 @@ vips_math2_const_buffer( VipsArithmetic *arithmetic,
 	int i, x, b;
 
 	switch( math2->math2 ) {
-	case VIPS_OPERATION_MATH2_POW: 	SWITCH( LOOPC, POW ); break;
-	case VIPS_OPERATION_MATH2_WOP: 	SWITCH( LOOPC, WOP ); break;
+	case VIPS_OPERATION_MATH2_POW: 	
+		SWITCH( LOOPC, POW ); 
+		break;
+
+	case VIPS_OPERATION_MATH2_WOP: 	
+		SWITCH( LOOPC, WOP ); 
+		break;
 
         default:
 		g_assert_not_reached();
+		break;
         }
 }
 
@@ -415,7 +421,7 @@ vips_math2_const_init( VipsMath2Const *math2_const )
 
 static int
 vips_math2_constv( VipsImage *in, VipsImage **out, 
-	VipsOperationMath2 math2, double *c, int n, va_list ap )
+	double *c, int n, VipsOperationMath2 math2, va_list ap )
 {
 	VipsArea *area_c;
 	double *array; 
@@ -427,7 +433,7 @@ vips_math2_constv( VipsImage *in, VipsImage **out,
 	for( i = 0; i < n; i++ ) 
 		array[i] = c[i];
 
-	result = vips_call_split( "math2_const", ap, in, out, math2, area_c );
+	result = vips_call_split( "math2_const", ap, in, out, area_c, math2 );
 
 	vips_area_unref( area_c );
 
@@ -438,9 +444,9 @@ vips_math2_constv( VipsImage *in, VipsImage **out,
  * vips_math2_const:
  * @in: input image
  * @out: output image
- * @math2: math operation to perform
  * @c: array of constants 
  * @n: number of constants in @c
+ * @math2: math operation to perform
  * @...: %NULL-terminated list of optional named arguments
  *
  * This operation calculates various 2-ary maths operations on an image and 
@@ -465,13 +471,13 @@ vips_math2_constv( VipsImage *in, VipsImage **out,
  */
 int
 vips_math2_const( VipsImage *in, VipsImage **out, 
-	VipsOperationMath2 math2, double *c, int n, ... )
+	double *c, int n, VipsOperationMath2 math2, ... )
 {
 	va_list ap;
 	int result;
 
-	va_start( ap, n );
-	result = vips_math2_constv( in, out, math2, c, n, ap ); 
+	va_start( ap, math2 );
+	result = vips_math2_constv( in, out, c, n, math2, ap ); 
 	va_end( ap );
 
 	return( result );
@@ -498,7 +504,7 @@ vips_pow_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_math2_constv( in, out, 
-		VIPS_OPERATION_MATH2_POW, c, n, ap );
+		c, n, VIPS_OPERATION_MATH2_POW, ap );
 	va_end( ap );
 
 	return( result );
@@ -525,7 +531,7 @@ vips_wop_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_math2_constv( in, out, 
-		VIPS_OPERATION_MATH2_WOP, c, n, ap );
+		c, n, VIPS_OPERATION_MATH2_WOP, ap );
 	va_end( ap );
 
 	return( result );
@@ -546,13 +552,13 @@ vips_wop_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
  */
 int
 vips_math2_const1( VipsImage *in, VipsImage **out, 
-	VipsOperationMath2 math2, double c, ... )
+	double c, VipsOperationMath2 math2, ... )
 {
 	va_list ap;
 	int result;
 
-	va_start( ap, c );
-	result = vips_math2_constv( in, out, math2, &c, 1, ap ); 
+	va_start( ap, math2 );
+	result = vips_math2_constv( in, out, &c, 1, math2, ap ); 
 	va_end( ap );
 
 	return( result );
@@ -578,7 +584,7 @@ vips_pow_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_math2_constv( in, out, 
-		VIPS_OPERATION_MATH2_POW, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_MATH2_POW, ap );
 	va_end( ap );
 
 	return( result );
@@ -604,7 +610,7 @@ vips_wop_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_math2_constv( in, out, 
-		VIPS_OPERATION_MATH2_WOP, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_MATH2_WOP, ap );
 	va_end( ap );
 
 	return( result );
diff --git a/libvips/arithmetic/relational.c b/libvips/arithmetic/relational.c
index 96dda30d..1898c8e1 100644
--- a/libvips/arithmetic/relational.c
+++ b/libvips/arithmetic/relational.c
@@ -574,7 +574,7 @@ vips_relational_const_init( VipsRelationalConst *relational_const )
 
 static int
 vips_relational_constv( VipsImage *in, VipsImage **out, 
-	VipsOperationRelational relational, double *c, int n, va_list ap )
+	double *c, int n, VipsOperationRelational relational, va_list ap )
 {
 	VipsArea *area_c;
 	double *array; 
@@ -587,7 +587,7 @@ vips_relational_constv( VipsImage *in, VipsImage **out,
 		array[i] = c[i];
 
 	result = vips_call_split( "relational_const", ap, 
-		in, out, relational, area_c );
+		in, out, area_c, relational );
 
 	vips_area_unref( area_c );
 
@@ -598,9 +598,9 @@ vips_relational_constv( VipsImage *in, VipsImage **out,
  * vips_relational_const:
  * @in: input image
  * @out: output image
- * @relational: relational operation to perform
  * @c: array of constants 
  * @n: number of constants in @c
+ * @relational: relational operation to perform
  * @...: %NULL-terminated list of optional named arguments
  *
  * Perform various relational operations on an image and an array of
@@ -621,13 +621,13 @@ vips_relational_constv( VipsImage *in, VipsImage **out,
  */
 int
 vips_relational_const( VipsImage *in, VipsImage **out, 
-	VipsOperationRelational relational, double *c, int n, ... )
+	double *c, int n, VipsOperationRelational relational, ... )
 {
 	va_list ap;
 	int result;
 
-	va_start( ap, n );
-	result = vips_relational_constv( in, out, relational, c, n, ap );
+	va_start( ap, relational );
+	result = vips_relational_constv( in, out, c, n, relational, ap );
 	va_end( ap );
 
 	return( result );
@@ -654,7 +654,7 @@ vips_equal_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_EQUAL, c, n, ap );
+		c, n, VIPS_OPERATION_RELATIONAL_EQUAL, ap );
 	va_end( ap );
 
 	return( result );
@@ -681,7 +681,7 @@ vips_notequal_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_NOTEQ, c, n, ap );
+		c, n, VIPS_OPERATION_RELATIONAL_NOTEQ, ap );
 	va_end( ap );
 
 	return( result );
@@ -708,7 +708,7 @@ vips_less_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_LESS, c, n, ap );
+		c, n, VIPS_OPERATION_RELATIONAL_LESS, ap );
 	va_end( ap );
 
 	return( result );
@@ -735,7 +735,7 @@ vips_lesseq_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_LESSEQ, c, n, ap );
+		c, n, VIPS_OPERATION_RELATIONAL_LESSEQ, ap );
 	va_end( ap );
 
 	return( result );
@@ -762,7 +762,7 @@ vips_more_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_MORE, c, n, ap );
+		c, n, VIPS_OPERATION_RELATIONAL_MORE, ap );
 	va_end( ap );
 
 	return( result );
@@ -789,7 +789,7 @@ vips_moreeq_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 
 	va_start( ap, n );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_MOREEQ, c, n, ap );
+		c, n, VIPS_OPERATION_RELATIONAL_MOREEQ, ap );
 	va_end( ap );
 
 	return( result );
@@ -799,8 +799,8 @@ vips_moreeq_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
  * vips_relational_const1:
  * @in: input image
  * @out: output image
- * @relational: relational operation to perform
  * @c: constant 
+ * @relational: relational operation to perform
  * @...: %NULL-terminated list of optional named arguments
  *
  * Perform various relational operations on an image and a constant. See
@@ -812,13 +812,13 @@ vips_moreeq_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
  */
 int
 vips_relational_const1( VipsImage *in, VipsImage **out, 
-	VipsOperationRelational relational, double c, ... )
+	double c, VipsOperationRelational relational, ... )
 {
 	va_list ap;
 	int result;
 
-	va_start( ap, c );
-	result = vips_relational_constv( in, out, relational, &c, 1, ap );
+	va_start( ap, relational );
+	result = vips_relational_constv( in, out, &c, 1, relational, ap );
 	va_end( ap );
 
 	return( result );
@@ -844,7 +844,7 @@ vips_equal_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_EQUAL, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_RELATIONAL_EQUAL, ap );
 	va_end( ap );
 
 	return( result );
@@ -870,7 +870,7 @@ vips_notequal_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_NOTEQ, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_RELATIONAL_NOTEQ, ap );
 	va_end( ap );
 
 	return( result );
@@ -896,7 +896,7 @@ vips_less_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_LESS, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_RELATIONAL_LESS, ap );
 	va_end( ap );
 
 	return( result );
@@ -922,7 +922,7 @@ vips_lesseq_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_LESSEQ, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_RELATIONAL_LESSEQ, ap );
 	va_end( ap );
 
 	return( result );
@@ -948,7 +948,7 @@ vips_more_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_MORE, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_RELATIONAL_MORE, ap );
 	va_end( ap );
 
 	return( result );
@@ -974,7 +974,7 @@ vips_moreeq_const1( VipsImage *in, VipsImage **out, double c, ... )
 
 	va_start( ap, c );
 	result = vips_relational_constv( in, out, 
-		VIPS_OPERATION_RELATIONAL_MOREEQ, &c, 1, ap );
+		&c, 1, VIPS_OPERATION_RELATIONAL_MOREEQ, ap );
 	va_end( ap );
 
 	return( result );
diff --git a/libvips/arithmetic/unaryconst.c b/libvips/arithmetic/unaryconst.c
index e95dc78e..a3eacad7 100644
--- a/libvips/arithmetic/unaryconst.c
+++ b/libvips/arithmetic/unaryconst.c
@@ -203,7 +203,7 @@ vips_unary_const_class_init( VipsUnaryConstClass *class )
 	object_class->description = _( "unary operations with a constant" );
 	object_class->build = vips_unary_const_build;
 
-	VIPS_ARG_BOXED( class, "c", 200, 
+	VIPS_ARG_BOXED( class, "c", 199, 
 		_( "c" ), 
 		_( "Array of constants" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
diff --git a/libvips/conversion/conversion.c b/libvips/conversion/conversion.c
index b0ed5e80..5441779b 100644
--- a/libvips/conversion/conversion.c
+++ b/libvips/conversion/conversion.c
@@ -196,7 +196,7 @@ vips_conversion_class_init( VipsConversionClass *class )
 	vobject_class->description = _( "conversion operations" );
 	vobject_class->build = vips_conversion_build;
 
-	VIPS_ARG_IMAGE( class, "out", 1, 
+	VIPS_ARG_IMAGE( class, "out", 2, 
 		_( "Output" ), 
 		_( "Output image" ),
 		VIPS_ARGUMENT_REQUIRED_OUTPUT, 
diff --git a/libvips/conversion/embed.c b/libvips/conversion/embed.c
index 14c1071d..e7a1265e 100644
--- a/libvips/conversion/embed.c
+++ b/libvips/conversion/embed.c
@@ -559,41 +559,41 @@ vips_embed_class_init( VipsEmbedClass *class )
 
 	operation_class->flags = VIPS_OPERATION_SEQUENTIAL_UNBUFFERED;
 
-	VIPS_ARG_IMAGE( class, "in", -1, 
+	VIPS_ARG_IMAGE( class, "in", 1, 
 		_( "Input" ), 
 		_( "Input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsEmbed, in ) );
 
-	VIPS_ARG_INT( class, "x", 2, 
+	VIPS_ARG_INT( class, "x", 3, 
 		_( "x" ), 
 		_( "Left edge of input in output" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsEmbed, x ),
 		-1000000000, 1000000000, 0 );
 
-	VIPS_ARG_INT( class, "y", 3, 
+	VIPS_ARG_INT( class, "y", 4, 
 		_( "y" ), 
 		_( "Top edge of input in output" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsEmbed, y ),
 		-1000000000, 1000000000, 0 );
 
-	VIPS_ARG_INT( class, "width", 4, 
+	VIPS_ARG_INT( class, "width", 5, 
 		_( "Width" ), 
 		_( "Image width in pixels" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsEmbed, width ),
 		1, 1000000000, 1 );
 
-	VIPS_ARG_INT( class, "height", 5, 
+	VIPS_ARG_INT( class, "height", 6, 
 		_( "Height" ), 
 		_( "Image height in pixels" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsEmbed, height ),
 		1, 1000000000, 1 );
 
-	VIPS_ARG_ENUM( class, "extend", 6, 
+	VIPS_ARG_ENUM( class, "extend", 7, 
 		_( "Extend" ), 
 		_( "How to generate the extra pixels" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
diff --git a/libvips/conversion/extract.c b/libvips/conversion/extract.c
index 6042a2cc..13e1b540 100644
--- a/libvips/conversion/extract.c
+++ b/libvips/conversion/extract.c
@@ -190,34 +190,34 @@ vips_extract_area_class_init( VipsExtractAreaClass *class )
 
 	operation_class->flags = VIPS_OPERATION_SEQUENTIAL_UNBUFFERED;
 
-	VIPS_ARG_IMAGE( class, "input", 0, 
+	VIPS_ARG_IMAGE( class, "input", 1, 
 		_( "Input" ), 
 		_( "Input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsExtractArea, in ) );
 
-	VIPS_ARG_INT( class, "left", 2, 
+	VIPS_ARG_INT( class, "left", 3, 
 		_( "Left" ), 
 		_( "Left edge of extract area" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsExtractArea, left ),
 		-VIPS_MAX_COORD, VIPS_MAX_COORD, 0 );
 
-	VIPS_ARG_INT( class, "top", 3, 
+	VIPS_ARG_INT( class, "top", 4, 
 		_( "Top" ), 
 		_( "Top edge of extract area" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsExtractArea, top ),
 		-VIPS_MAX_COORD, VIPS_MAX_COORD, 0 );
 
-	VIPS_ARG_INT( class, "width", 4, 
+	VIPS_ARG_INT( class, "width", 5, 
 		_( "Width" ), 
 		_( "Width of extract area" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsExtractArea, width ),
 		1, VIPS_MAX_COORD, 1 );
 
-	VIPS_ARG_INT( class, "height", 5, 
+	VIPS_ARG_INT( class, "height", 6, 
 		_( "Height" ), 
 		_( "Height of extract area" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
@@ -413,7 +413,7 @@ vips_extract_band_class_init( VipsExtractBandClass *class )
 
 	bandary_class->process_line = vips_extract_band_buffer;
 
-	VIPS_ARG_IMAGE( class, "in", 0, 
+	VIPS_ARG_IMAGE( class, "in", 1, 
 		_( "Input" ), 
 		_( "Input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
diff --git a/libvips/conversion/gamma.c b/libvips/conversion/gamma.c
index 91fe63af..94b80559 100644
--- a/libvips/conversion/gamma.c
+++ b/libvips/conversion/gamma.c
@@ -139,13 +139,13 @@ vips_gamma_class_init( VipsGammaClass *class )
 
 	operation_class->flags = VIPS_OPERATION_SEQUENTIAL_UNBUFFERED;
 
-	VIPS_ARG_IMAGE( class, "in", -1, 
+	VIPS_ARG_IMAGE( class, "in", 1, 
 		_( "in" ), 
 		_( "Input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsGamma, in ) );
 
-	VIPS_ARG_DOUBLE( class, "exponent", 0, 
+	VIPS_ARG_DOUBLE( class, "exponent", 2, 
 		_( "exponent" ), 
 		_( "Gamma factor" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
diff --git a/libvips/conversion/insert.c b/libvips/conversion/insert.c
index 1e4dd668..324ab0d2 100644
--- a/libvips/conversion/insert.c
+++ b/libvips/conversion/insert.c
@@ -508,40 +508,40 @@ vips_insert_class_init( VipsInsertClass *class )
 	 */
 	operation_class->flags = VIPS_OPERATION_SEQUENTIAL;
 
-	VIPS_ARG_IMAGE( class, "main", -1, 
+	VIPS_ARG_IMAGE( class, "main", 0, 
 		_( "Main" ), 
 		_( "Main input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsInsert, main ) );
 
-	VIPS_ARG_IMAGE( class, "sub", 0, 
+	VIPS_ARG_IMAGE( class, "sub", 1, 
 		_( "Sub-image" ), 
 		_( "Sub-image to insert into main image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsInsert, sub ) );
 
-	VIPS_ARG_INT( class, "x", 2, 
+	VIPS_ARG_INT( class, "x", 3, 
 		_( "X" ), 
 		_( "Left edge of sub in main" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsInsert, x ),
 		-VIPS_MAX_COORD, VIPS_MAX_COORD, 0 );
 
-	VIPS_ARG_INT( class, "y", 3, 
+	VIPS_ARG_INT( class, "y", 4, 
 		_( "Y" ), 
 		_( "Top edge of sub in main" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsInsert, y ),
 		-VIPS_MAX_COORD, VIPS_MAX_COORD, 0 );
 
-	VIPS_ARG_BOOL( class, "expand", 4, 
+	VIPS_ARG_BOOL( class, "expand", 5, 
 		_( "Expand" ), 
 		_( "Expand output to hold all of both inputs" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
 		G_STRUCT_OFFSET( VipsInsert, expand ),
 		FALSE );
 
-	VIPS_ARG_BOXED( class, "background", 5, 
+	VIPS_ARG_BOXED( class, "background", 6, 
 		_( "Background" ), 
 		_( "Color for new pixels" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
diff --git a/libvips/conversion/join.c b/libvips/conversion/join.c
index 7c2ccc57..46b3c390 100644
--- a/libvips/conversion/join.c
+++ b/libvips/conversion/join.c
@@ -228,19 +228,19 @@ vips_join_class_init( VipsJoinClass *class )
 	vobject_class->description = _( "join a pair of images" );
 	vobject_class->build = vips_join_build;
 
-	VIPS_ARG_IMAGE( class, "in1", -1, 
+	VIPS_ARG_IMAGE( class, "in1", 0, 
 		_( "in1" ), 
 		_( "First input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsJoin, in1 ) );
 
-	VIPS_ARG_IMAGE( class, "in2", 0, 
+	VIPS_ARG_IMAGE( class, "in2", 1, 
 		_( "in2" ), 
 		_( "Second input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsJoin, in2 ) );
 
-	VIPS_ARG_ENUM( class, "direction", 2, 
+	VIPS_ARG_ENUM( class, "direction", 3, 
 		_( "direction" ), 
 		_( "Join left-right or up-down" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
@@ -268,7 +268,7 @@ vips_join_class_init( VipsJoinClass *class )
 		G_STRUCT_OFFSET( VipsJoin, background ),
 		VIPS_TYPE_ARRAY_DOUBLE );
 
-	VIPS_ARG_ENUM( class, "align", 2, 
+	VIPS_ARG_ENUM( class, "align", 7, 
 		_( "Align" ), 
 		_( "Align on the low, centre or high coordinate edge" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
diff --git a/libvips/conversion/subsample.c b/libvips/conversion/subsample.c
index 1fdfde8f..9c3d78fa 100644
--- a/libvips/conversion/subsample.c
+++ b/libvips/conversion/subsample.c
@@ -265,27 +265,27 @@ vips_subsample_class_init( VipsSubsampleClass *class )
 	 * scanlines, and that confuses vips_sequential().
 	 */
 
-	VIPS_ARG_IMAGE( class, "input", 0, 
+	VIPS_ARG_IMAGE( class, "input", 1, 
 		_( "Input" ), 
 		_( "Input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsSubsample, in ) );
 
-	VIPS_ARG_INT( class, "xfac", 2, 
+	VIPS_ARG_INT( class, "xfac", 3, 
 		_( "Xfac" ), 
 		_( "Horizontal subsample factor" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsSubsample, xfac ),
 		1, VIPS_MAX_COORD, 1 );
 
-	VIPS_ARG_INT( class, "yfac", 3, 
+	VIPS_ARG_INT( class, "yfac", 4, 
 		_( "Yfac" ), 
 		_( "Vertical subsample factor" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsSubsample, yfac ),
 		1, VIPS_MAX_COORD, 1 );
 
-	VIPS_ARG_BOOL( class, "point", 2, 
+	VIPS_ARG_BOOL( class, "point", 5, 
 		_( "Point" ), 
 		_( "Point sample" ),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
diff --git a/libvips/conversion/zoom.c b/libvips/conversion/zoom.c
index af6800e9..ca54b995 100644
--- a/libvips/conversion/zoom.c
+++ b/libvips/conversion/zoom.c
@@ -374,20 +374,20 @@ vips_zoom_class_init( VipsZoomClass *class )
 
 	operation_class->flags = VIPS_OPERATION_SEQUENTIAL_UNBUFFERED;
 
-	VIPS_ARG_IMAGE( class, "input", 0, 
+	VIPS_ARG_IMAGE( class, "input", 1, 
 		_( "Input" ), 
 		_( "Input image" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsZoom, in ) );
 
-	VIPS_ARG_INT( class, "xfac", 2, 
+	VIPS_ARG_INT( class, "xfac", 3, 
 		_( "Xfac" ), 
 		_( "Horizontal zoom factor" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
 		G_STRUCT_OFFSET( VipsZoom, xfac ),
 		1, VIPS_MAX_COORD, 1 );
 
-	VIPS_ARG_INT( class, "yfac", 3, 
+	VIPS_ARG_INT( class, "yfac", 4, 
 		_( "Yfac" ), 
 		_( "Vertical zoom factor" ),
 		VIPS_ARGUMENT_REQUIRED_INPUT,
diff --git a/libvips/deprecated/vips7compat.c b/libvips/deprecated/vips7compat.c
index 863fe701..29de1e09 100644
--- a/libvips/deprecated/vips7compat.c
+++ b/libvips/deprecated/vips7compat.c
@@ -2749,7 +2749,7 @@ vips__relational_vec( IMAGE *in, IMAGE *out,
 {
 	VipsImage *t;
 
-	if( vips_relational_const( in, &t, relational, c, n,
+	if( vips_relational_const( in, &t, c, n, relational, 
 		NULL ) )
 		return( -1 );
 	if( vips_image_write( t, out ) ) {
@@ -2921,7 +2921,7 @@ vips__boolean_vec( IMAGE *in, IMAGE *out,
 {
 	VipsImage *t;
 
-	if( vips_boolean_const( in, &t, boolean, c, n,
+	if( vips_boolean_const( in, &t, c, n, boolean,
 		NULL ) )
 		return( -1 );
 	if( vips_image_write( t, out ) ) {
@@ -3008,7 +3008,7 @@ vips__math2_vec( IMAGE *in, IMAGE *out,
 {
 	VipsImage *t;
 
-	if( vips_math2_const( in, &t, math2, c, n,
+	if( vips_math2_const( in, &t, c, n, math2, 
 		NULL ) )
 		return( -1 );
 	if( vips_image_write( t, out ) ) {
diff --git a/libvips/include/vips/arithmetic.h b/libvips/include/vips/arithmetic.h
index 7c42e2d3..ccee62f4 100644
--- a/libvips/include/vips/arithmetic.h
+++ b/libvips/include/vips/arithmetic.h
@@ -279,7 +279,7 @@ int vips_more( VipsImage *left, VipsImage *right, VipsImage **out, ... )
 int vips_moreeq( VipsImage *left, VipsImage *right, VipsImage **out, ... )
 	__attribute__((sentinel));
 int vips_relational_const( VipsImage *in, VipsImage **out, 
-	VipsOperationRelational relational, double *c, int n, ... )
+	double *c, int n, VipsOperationRelational relational, ... )
 	__attribute__((sentinel));
 int vips_equal_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 	__attribute__((sentinel));
@@ -294,7 +294,7 @@ int vips_more_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 int vips_moreeq_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 	__attribute__((sentinel));
 int vips_relational_const1( VipsImage *in, VipsImage **out, 
-	VipsOperationRelational relational, double c, ... )
+	double c, VipsOperationRelational relational, ... )
 	__attribute__((sentinel));
 int vips_equal_const1( VipsImage *in, VipsImage **out, double c, ... )
 	__attribute__((sentinel));
@@ -324,7 +324,7 @@ int vips_rshift( VipsImage *left, VipsImage *right, VipsImage **out, ... )
 	__attribute__((sentinel));
 
 int vips_boolean_const( VipsImage *in, VipsImage **out, 
-	VipsOperationBoolean boolean, double *c, int n, ... )
+	double *c, int n, VipsOperationBoolean boolean, ... )
 	__attribute__((sentinel));
 int vips_andimage_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 	__attribute__((sentinel));
@@ -337,7 +337,7 @@ int vips_lshift_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 int vips_rshift_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 	__attribute__((sentinel));
 int vips_boolean_const1( VipsImage *in, VipsImage **out, 
-	VipsOperationBoolean boolean, double c, ... )
+	double c, VipsOperationBoolean boolean, ... )
 	__attribute__((sentinel));
 int vips_andimage_const1( VipsImage *in, VipsImage **out, double c, ... )
 	__attribute__((sentinel));
@@ -358,14 +358,14 @@ int vips_pow( VipsImage *left, VipsImage *right, VipsImage **out, ... )
 int vips_wop( VipsImage *left, VipsImage *right, VipsImage **out, ... )
 	__attribute__((sentinel));
 int vips_math2_const( VipsImage *in, VipsImage **out, 
-	VipsOperationMath2 math2, double *c, int n, ... )
+	double *c, int n, VipsOperationMath2 math2, ... )
 	__attribute__((sentinel));
 int vips_pow_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 	__attribute__((sentinel));
 int vips_wop_const( VipsImage *in, VipsImage **out, double *c, int n, ... )
 	__attribute__((sentinel));
 int vips_math2_const1( VipsImage *in, VipsImage **out, 
-	VipsOperationMath2 math2, double c, ... )
+	double c, VipsOperationMath2 math2, ... )
 	__attribute__((sentinel));
 int vips_pow_const1( VipsImage *in, VipsImage **out, double c, ... )
 	__attribute__((sentinel));
diff --git a/libvips/iofuncs/object.c b/libvips/iofuncs/object.c
index 77841dcc..318d3f7f 100644
--- a/libvips/iofuncs/object.c
+++ b/libvips/iofuncs/object.c
@@ -1661,6 +1661,20 @@ vips_object_init( VipsObject *object )
 	g_mutex_unlock( vips__object_all_lock );
 }
 
+static void *
+traverse_find_required_priority( void *data, void *a, void *b )
+{
+	VipsArgumentClass *argument_class = (VipsArgumentClass *) data;
+	int priority = GPOINTER_TO_INT( a ); 
+
+	if( (argument_class->flags & VIPS_ARGUMENT_REQUIRED) && 
+		!(argument_class->flags & VIPS_ARGUMENT_DEPRECATED) && 
+		argument_class->priority == priority )
+		return( argument_class );
+	
+	return( NULL ); 
+}
+
 static gint
 traverse_sort( gconstpointer a, gconstpointer b )
 {
@@ -1677,7 +1691,9 @@ vips_object_class_install_argument( VipsObjectClass *object_class,
 	GParamSpec *pspec, VipsArgumentFlags flags, int priority, guint offset )
 {
 	VipsArgumentClass *argument_class = g_new( VipsArgumentClass, 1 );
+
 	GSList *argument_table_traverse;
+	VipsArgumentClass *ac;
 
 #ifdef DEBUG
 	printf( "vips_object_class_install_argument: %p %s %s\n", 
@@ -1731,6 +1747,21 @@ vips_object_class_install_argument( VipsObjectClass *object_class,
 	argument_table_traverse = 
 		g_slist_copy( object_class->argument_table_traverse );
 
+	/* We keep traverse sorted by priority, so we musn't have duplicate
+	 * priority values in required args. 
+	 */
+	if( (flags & VIPS_ARGUMENT_REQUIRED) && 
+		!(flags & VIPS_ARGUMENT_DEPRECATED) && 
+		(ac = vips_slist_map2( argument_table_traverse,
+			traverse_find_required_priority, 
+			GINT_TO_POINTER( priority ), NULL )) ) 
+		g_warning( "vips_object_class_install_argument: "
+			"%s.%s, %s.%s duplicate priority", 
+			g_type_name( G_TYPE_FROM_CLASS( object_class ) ),
+			g_param_spec_get_name( pspec ),
+			g_type_name( G_TYPE_FROM_CLASS( ac->object_class ) ),
+			g_param_spec_get_name( ((VipsArgument *) ac)->pspec ) ); 
+
 	argument_table_traverse = g_slist_prepend(
 		argument_table_traverse, argument_class );
 	argument_table_traverse = g_slist_sort(