diff --git a/libvips/colour/colour.c b/libvips/colour/colour.c
index 824824b6..4c7c48f9 100644
--- a/libvips/colour/colour.c
+++ b/libvips/colour/colour.c
@@ -56,9 +56,9 @@ vips_colour_gen( VipsRegion *or,
 	Rect *r = &or->valid;
 
 	VipsPel *p, *q;
-	int i, y;
+	int y;
 
-	if( vips_region_prepare( ir[i], r ) ) 
+	if( vips_region_prepare( ir, r ) ) 
 		return( -1 );
 	p = (VipsPel *) VIPS_REGION_ADDR( ir, r->left, r->top );
 	q = (VipsPel *) VIPS_REGION_ADDR( or, r->left, r->top );
@@ -77,7 +77,8 @@ static int
 vips_colour_build( VipsObject *object )
 {
 	VipsColour *colour = VIPS_COLOUR( object );
-	VipsColourClass *aclass = VIPS_COLOUR_GET_CLASS( colour );
+
+	VipsImage **t;
 
 #ifdef DEBUG
 	printf( "vips_colour_build: " );
@@ -91,16 +92,53 @@ vips_colour_build( VipsObject *object )
 
 	g_object_set( colour, "out", vips_image_new(), NULL ); 
 
-	if( vips_image_copy_fields( colour->out, colour->in ) ) 
+	if( vips_image_pio_input( colour->in ) || 
+		vips_check_bands_1or3( "VipsColour", colour->in ) ||
+		vips_check_uncoded( "VipsColour", colour->in ) ) 
 		return( -1 );
-        vips_demand_hint( colour->out, 
-		VIPS_DEMAND_STYLE_THINSTRIP, colour->in, NULL );
 
-	if( vips_image_generate( colour->out,
-		vips_start_one, vips_colour_gen, vips_stop_one, 
-		colour->in, colour ) ) 
+	t = (VipsImage **) vips_object_local_array( object, 5 );
+
+	/* Always process float.
+	 */
+	if( vips_cast_float( colour->in, &t[0], NULL ) )
 		return( -1 );
 
+	/* If there are more than bands, process just the first three and
+	 * reattach the rest after.
+	 */
+	if( t[0]->Bands > 3 ) {
+		if( vips_extract_band( t[0], &t[1], 0, "n", 3, NULL ) ||
+			vips_extract_band( t[0], &t[2], 0, 
+				"n", t[0]->Bands - 3, NULL ) )
+			return( -1 );
+
+		if( vips_image_copy_fields( t[3], t[1] ) ) 
+			return( -1 );
+		vips_demand_hint( t[3], 
+			VIPS_DEMAND_STYLE_THINSTRIP, t[1], NULL );
+
+		if( vips_image_generate( t[3],
+			vips_start_one, vips_colour_gen, vips_stop_one, 
+			t[1], colour ) ) 
+			return( -1 );
+
+		if( vips_bandjoin2( t[3], t[2], &t[4], NULL ) ||
+			vips_image_write( t[4], colour->out ) )
+			return( -1 );
+	}
+	else {
+		if( vips_image_copy_fields( colour->out, t[1] ) ) 
+			return( -1 );
+		vips_demand_hint( colour->out, 
+			VIPS_DEMAND_STYLE_THINSTRIP, t[1], NULL );
+
+		if( vips_image_generate( colour->out,
+			vips_start_one, vips_colour_gen, vips_stop_one, 
+			t[1], colour ) ) 
+			return( -1 );
+	}
+
 	return( 0 );
 }
 
diff --git a/libvips/include/vips/error.h b/libvips/include/vips/error.h
index 2681efae..27695213 100644
--- a/libvips/include/vips/error.h
+++ b/libvips/include/vips/error.h
@@ -62,8 +62,9 @@ int vips_check_coding_rad( const char *domain, VipsImage *im );
 int vips_check_coding_noneorlabq( const char *domain, VipsImage *im );
 int vips_check_coding_same( const char *domain, VipsImage *im1, VipsImage *im2 );
 int vips_check_mono( const char *domain, VipsImage *im );
-int vips_check_bands_1or3( const char *domain, VipsImage *in );
 int vips_check_bands( const char *domain, VipsImage *im, int bands );
+int vips_check_bands_1or3( const char *domain, VipsImage *in );
+int vips_check_bands_3ormore( const char *domain, VipsImage *im );
 int vips_check_bands_1orn( const char *domain, VipsImage *im1, VipsImage *im2 );
 int vips_check_bands_1orn_unary( const char *domain, VipsImage *im, int n );
 int vips_check_bands_same( const char *domain, VipsImage *im1, VipsImage *im2 );
diff --git a/libvips/iofuncs/error.c b/libvips/iofuncs/error.c
index b6ee8530..257954af 100644
--- a/libvips/iofuncs/error.c
+++ b/libvips/iofuncs/error.c
@@ -606,7 +606,7 @@ vips_check_bands( const char *domain, VipsImage *im, int bands )
 }
 
 /**
- * vips_check_1or3:
+ * vips_check_bands_1or3:
  * @domain: the originating domain for the error message
  * @im: image to check
  *
@@ -630,6 +630,31 @@ vips_check_bands_1or3( const char *domain, VipsImage *im )
 	return( 0 );
 }
 
+/**
+ * vips_check_bands_3ormore:
+ * @domain: the originating domain for the error message
+ * @im: image to check
+ *
+ * Check that the image has at least three bands. 
+ * Otherwise set an error message
+ * and return non-zero.
+ *
+ * See also: vips_error().
+ *
+ * Returns: 0 if OK, -1 otherwise.
+ */
+int
+vips_check_bands_3ormore( const char *domain, VipsImage *im )
+{
+	if( im->Bands < 3 ) {
+		vips_error( domain, "%s", 
+			_( "image must have at least three bands" ) );
+		return( -1 );
+	}
+
+	return( 0 );
+}
+
 /**
  * vips_check_bands_1orn:
  * @domain: the originating domain for the error message
diff --git a/libvips/iofuncs/object.c b/libvips/iofuncs/object.c
index e3537d8a..0add3a6b 100644
--- a/libvips/iofuncs/object.c
+++ b/libvips/iofuncs/object.c
@@ -349,9 +349,6 @@ void *
 vips_argument_map( VipsObject *object,
 	VipsArgumentMapFn fn, void *a, void *b )
 {
-	VipsObjectClass *object_class = VIPS_OBJECT_GET_CLASS( object ); 
-	GSList *p; 
-
 	/* Make sure we can't go during the loop. This can happen if eg. we
 	 * flush an arg that refs us.
 	 */
@@ -370,7 +367,7 @@ vips_argument_map( VipsObject *object,
 			g_object_unref( object ); 
 			return( result );
 		}
-	}
+	} VIPS_ARGUMENT_FOR_ALL_END
 
 	g_object_unref( object );