diff --git a/libvips/include/vips/error.h b/libvips/include/vips/error.h
index 47155e58..2681efae 100644
--- a/libvips/include/vips/error.h
+++ b/libvips/include/vips/error.h
@@ -83,6 +83,7 @@ int vips_check_vector( const char *domain, int n, VipsImage *im );
 int vips_check_hist( const char *domain, VipsImage *im );
 int vips_check_imask( const char *domain, INTMASK *mask );
 int vips_check_dmask( const char *domain, DOUBLEMASK *mask );
+int vips_check_dmask_1d( const char *domain, DOUBLEMASK *mask );
 
 #ifdef __cplusplus
 }
diff --git a/libvips/iofuncs/error.c b/libvips/iofuncs/error.c
index 31c22f2c..d36b078d 100644
--- a/libvips/iofuncs/error.c
+++ b/libvips/iofuncs/error.c
@@ -1153,3 +1153,28 @@ vips_check_dmask( const char *domain, DOUBLEMASK *mask )
 
 	return( 0 );
 }
+
+/**
+ * vips_check_dmask_1d:
+ * @domain: the originating domain for the error message
+ * @mask: mask to check
+ *
+ * A mask must be one-dimensional (width or height 1).
+ *
+ * See also: vips_error().
+ *
+ * Returns: 0 if OK, -1 otherwise.
+ */
+int
+vips_check_dmask_1d( const char *domain, DOUBLEMASK *mask )
+{
+	if( vips_check_dmask( domain, mask ) )
+		return( -1 );
+	if( mask->xsize != 1 &&
+		mask->ysize != 1 ) {
+		vips_error( domain, "%s", _( "mask must be 1D" ) );
+		return( -1 );
+	}
+
+	return( 0 );
+}