diff --git a/ChangeLog b/ChangeLog
index 083c278b..ba8b4e76 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -4,6 +4,7 @@
 - configure spots support for "restrict"
 - reset dcm:display-range on magick read to help DICOM
 - saner im_buildlut() behaviour
+- added im_gauss_imask_sep() 
 
 3/3/09 started 7.17.2
 - im_magick2vips.c: allow funky bit depths, like 14 (thanks Mikkel)
diff --git a/include/vips/proto.h b/include/vips/proto.h
index eff14860..53dd15ba 100644
--- a/include/vips/proto.h
+++ b/include/vips/proto.h
@@ -234,6 +234,7 @@ DOUBLEMASK *im_rotate_dmask45( DOUBLEMASK *, const char * );
 INTMASK *im_log_imask( const char *, double, double );
 DOUBLEMASK *im_log_dmask( const char *, double, double );
 INTMASK *im_gauss_imask( const char *, double, double );
+INTMASK *im_gauss_imask_sep( const char *, double, double );
 DOUBLEMASK *im_gauss_dmask( const char *, double, double );
 
 int im_rank( IMAGE *, IMAGE *, int, int, int );
diff --git a/libsrc/convolution/convol_dispatch.c b/libsrc/convolution/convol_dispatch.c
index dde2e737..a5b16d90 100644
--- a/libsrc/convolution/convol_dispatch.c
+++ b/libsrc/convolution/convol_dispatch.c
@@ -672,6 +672,33 @@ static im_function gauss_imask_desc = {
 	gauss_imask_args 		/* Arg list */
 };
 
+/* Call im_gauss_imask_sep via arg vector.
+ */
+static int
+gauss_imask_sep_vec( im_object *argv )
+{
+	im_mask_object *mo = argv[0];
+	double sigma = *((double *) argv[1]);
+	double min_amp = *((double *) argv[2]);
+
+	if( !(mo->mask = 
+		im_gauss_imask_sep( mo->name, sigma, min_amp )) )
+		return( -1 );
+	
+	return( 0 );
+}
+
+/* Description of im_gauss_imask_sep.
+ */ 
+static im_function gauss_imask_sep_desc = {
+	"im_gauss_imask_sep", 		/* Name */
+	"generate separable gaussian INTMASK",
+	0,				/* Flags */
+	gauss_imask_sep_vec, 		/* Dispatch function */
+	IM_NUMBER( gauss_imask_args ), 	/* Size of arg list */
+	gauss_imask_args 		/* Arg list */
+};
+
 /* Args for im_gaussnoise.
  */
 static im_arg_desc gaussnoise_args[] = {
@@ -1347,6 +1374,7 @@ static im_function *convol_list[] = {
 	&fastcor_raw_desc,
 	&gauss_dmask_desc,
 	&gauss_imask_desc,
+	&gauss_imask_sep_desc,
 	&gaussnoise_desc,
         &grad_x_desc,
         &grad_y_desc,
diff --git a/libsrc/convolution/im_gaussmasks.c b/libsrc/convolution/im_gaussmasks.c
index 3402ccab..c752daea 100644
--- a/libsrc/convolution/im_gaussmasks.c
+++ b/libsrc/convolution/im_gaussmasks.c
@@ -27,6 +27,9 @@
  *	- ansified, mem leaks plugged
  * 20/11/98 JC
  *	- mask too large check added
+ * 18/3/09
+ * 	- bumped max mask size *40
+ * 	- added _sep variant
  */
 
 /*
@@ -69,7 +72,7 @@
 #include <dmalloc.h>
 #endif /*WITH_DMALLOC*/
 
-#define IM_MAXMASK 256
+#define IM_MAXMASK 5000
 
 DOUBLEMASK *
 im_gauss_dmask( const char *filename, double sigma, double min_ampl )
@@ -96,7 +99,7 @@ im_gauss_dmask( const char *filename, double sigma, double min_ampl )
 			break;
 	}
 	if( x == max_x ) {
-		im_errormsg( "im_gauss_dmask: mask too large" );
+		im_error( "im_gauss_dmask", "%s", _( "mask too large" ) );
 		return( NULL );
 	}
 
@@ -180,3 +183,28 @@ im_gauss_imask( const char *filename, double sigma, double min_amplitude )
 
 	return( im ) ;
 }
+
+/* Just return the central line of the mask. This helps nip, which really
+ * struggles with large matrix manipulations.
+ */
+INTMASK *
+im_gauss_imask_sep( const char *filename, double sigma, double min_amplitude )
+{
+	INTMASK *im;
+	INTMASK *im2;
+	int i;
+
+	if( !(im = im_gauss_imask( filename, sigma, min_amplitude )) )
+		return( NULL );
+	if( !(im2 = im_create_imask( filename, im->xsize, 1 )) ) {
+		im_free_imask( im );
+		return( NULL );
+	}
+
+	for( i = 0; i < im->xsize; i++ )
+		im2->coeff[i] = im->coeff[i + im->xsize * (im->ysize / 2)];
+
+	im_free_imask( im );
+
+	return( im2 ) ;
+}