diff --git a/libvips/arithmetic/im_max.c b/libvips/arithmetic/im_max.c
index d4c9c705..2713432d 100644
--- a/libvips/arithmetic/im_max.c
+++ b/libvips/arithmetic/im_max.c
@@ -240,12 +240,9 @@ im_max( IMAGE *in, double *out )
 	inf.out = out;
 	inf.valid = 0;
 
-	if( im_pincheck( in ) )
+	if( im_pincheck( in ) ||
+		im_check_uncoded( "im_max", in ) )
 		return( -1 );
-	if( in->Coding != IM_CODING_NONE ) {
-		im_error( "im_max", "%s", _( "not uncoded" ) );
-		return( -1 );
-	}
 
 	if( im_iterate( in, max_start, max_scan, max_stop, &inf, NULL ) ) 
 		return( -1 );
diff --git a/libvips/arithmetic/im_maxpos_avg.c b/libvips/arithmetic/im_maxpos_avg.c
index 5427aaa1..cdb799fb 100644
--- a/libvips/arithmetic/im_maxpos_avg.c
+++ b/libvips/arithmetic/im_maxpos_avg.c
@@ -1,14 +1,4 @@
-/* @(#) Function to find the maximum of an image.  Returns coords and value at
- * @(#) double precision.  In the event of a draw, returns average of all 
- * @(#) drawing coords, and interpolated value at that position.
- * @(#)
- * @(#) int im_maxpos_avg(
- * @(#)   IMAGE *im,
- * @(#)   double *xpos,
- * @(#)   double *ypos,
- * @(#)   double *out
- * @(#) );
- * @(#) 
+/* im_maxpos_avg.c
  *
  * Copyright: 2006, The Nottingham Trent University
  * Copyright: 2006, Tom Vajzovic
@@ -20,6 +10,8 @@
  * 	- changed spelling of occurrences
  * 	- check for !occurrences before using val
  * 	- renamed avg as sum, a bit clearer
+ * 2/9/09
+ * 	- gtkdoc comment
  */
 
 /*
@@ -83,30 +75,37 @@ static int maxpos_avg_stop( void *seq, void *, void * );
 
 /** EXPORTED FUNCTION **/
 
+/** 
+ * im_maxpos_avg:
+ * @im: image to scan
+ * @xpos: returned X position
+ * @ypos: returned Y position
+ * @out: returned value
+ *
+ * Function to find the maximum of an image.  Returns coords and value at
+ * double precision.  In the event of a draw, returns average of all 
+ * drawing coords, and interpolated value at that position.
+ *
+ * See also: im_maxpos(), im_min(), im_stats().
+ *
+ * Returns: 0 on success, -1 on error
+ */
 int im_maxpos_avg( IMAGE *im, double *xpos, double *ypos, double *out ){
 #define FUNCTION_NAME "im_maxpos_avg"
 
   pos_avg_t master= { 0.0, 0.0, 0.0, 0 };
 
-  if( im_pincheck( im ) )
+  if( im_pincheck( im ) ||
+    im_check_uncoded( FUNCTION_NAME, im ) ||
+    im_check_noncomplex( FUNCTION_NAME, im ) ||
+    im_check_mono( FUNCTION_NAME, im ) )
     return -1;
 
-  if( im-> Coding ){
-    im_error( FUNCTION_NAME, "%s", _("uncoded images only") );
-    return -1;
-  }
-  if( !( im_isint( im ) || im_isfloat( im ) ) ){
-    im_error( FUNCTION_NAME, "%s", _("scalar images only") );
-    return -1;
-  }
-  if( 1 != im-> Bands ){
-    im_error( FUNCTION_NAME, "%s", _("single band images only") );
-    return -1;
-  }
   if( ! xpos || ! ypos || ! out ){
     im_error( FUNCTION_NAME, "%s", _("invalid argument") );
     return -1;
   }
+
   if( im_iterate( im, maxpos_avg_start, maxpos_avg_scan, maxpos_avg_stop, &master, NULL ) )
     return -1;
 
diff --git a/libvips/include/vips/proto.h b/libvips/include/vips/proto.h
index 89856014..96447f01 100644
--- a/libvips/include/vips/proto.h
+++ b/libvips/include/vips/proto.h
@@ -141,6 +141,7 @@ int im_check_bands_1orn( const char *domain, IMAGE *im1, IMAGE *im2 );
 int im_check_noncomplex( const char *domain, IMAGE *im );
 int im_check_complex( const char *domain, IMAGE *im );
 int im_check_uchar( const char *domain, IMAGE *im );
+int im_check_mono( const char *domain, IMAGE *im );
 int im_check_int( const char *domain, IMAGE *im );
 int im_check_size( const char *domain, IMAGE *im1, IMAGE *im2 );
 int im_check_bands( const char *domain, IMAGE *im1, IMAGE *im2 );
diff --git a/libvips/iofuncs/predicate.c b/libvips/iofuncs/predicate.c
index d54e8710..313685e3 100644
--- a/libvips/iofuncs/predicate.c
+++ b/libvips/iofuncs/predicate.c
@@ -417,6 +417,17 @@ im_check_uchar( const char *domain, IMAGE *im )
 	return( 0 );
 }
 
+int
+im_check_mono( const char *domain, IMAGE *im )
+{
+	if( im->Bands != 1 ) {
+		im_error( domain, "%s", _( "image must one band" ) );
+		return( -1 );
+	}
+
+	return( 0 );
+}
+
 int
 im_check_int( const char *domain, IMAGE *im )
 {