diff --git a/ChangeLog b/ChangeLog
index a001674dd3..9e66488c40 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2005-09-07  Michael Natterer  <mitch@gimp.org>
+
+	* app/core/gimpchannel-combine.c (gimp_channel_combine_ellipse):
+	use gimp_rectangle_intersect() instead of just looking at the
+	passed in w,h to figure whether nothing needs to be done. While
+	the algorithm does nicely with an entirely out-of-image ellipse,
+	the channel's bounds were set to a rectangle of zero width or
+	height, which caused subsequent calls to gimp_channel_bounds() to
+	return broken bounds. Fixes bug #315417.
+
+	(gimp_channel_combine_rect)
+	(gimp_channel_combine_mask): use gimp_rectangle_intersect() here
+	too instead of the usual unclear CLAMPing on x1,y1,x2,y2.
+
 2005-09-07  Ankit Patel  <ankit644@yahoo.com>
 
 	* configure.in: Added 'gu' to ALL_LINGUAS.
diff --git a/app/core/gimpchannel-combine.c b/app/core/gimpchannel-combine.c
index c8ec99374f..d1d810d56f 100644
--- a/app/core/gimpchannel-combine.c
+++ b/app/core/gimpchannel-combine.c
@@ -27,6 +27,7 @@
 #include "base/pixel-processor.h"
 #include "base/pixel-region.h"
 
+#include "gimp-utils.h"
 #include "gimpchannel.h"
 #include "gimpchannel-combine.h"
 
@@ -130,24 +131,16 @@ gimp_channel_combine_rect (GimpChannel    *mask,
 			   gint            w,
 			   gint            h)
 {
-  gint        x2, y2;
   PixelRegion maskPR;
   guchar      color;
 
   g_return_if_fail (GIMP_IS_CHANNEL (mask));
 
-  y2 = y + h;
-  x2 = x + w;
-
-  x  = CLAMP (x,  0, GIMP_ITEM (mask)->width);
-  y  = CLAMP (y,  0, GIMP_ITEM (mask)->height);
-  x2 = CLAMP (x2, 0, GIMP_ITEM (mask)->width);
-  y2 = CLAMP (y2, 0, GIMP_ITEM (mask)->height);
-
-  w = x2 - x;
-  h = y2 - y;
-
-  if (w <= 0 || h <= 0)
+  if (! gimp_rectangle_intersect (x, y, w, h,
+                                  0, 0,
+                                  GIMP_ITEM (mask)->width,
+                                  GIMP_ITEM (mask)->height,
+                                  &x, &y, &w, &h))
     return;
 
   pixel_region_init (&maskPR, GIMP_DRAWABLE (mask)->tiles,
@@ -225,7 +218,11 @@ gimp_channel_combine_ellipse (GimpChannel    *mask,
 
   g_return_if_fail (GIMP_IS_CHANNEL (mask));
 
-  if (!w || !h)
+  if (! gimp_rectangle_intersect (x, y, w, h,
+                                  0, 0,
+                                  GIMP_ITEM (mask)->width,
+                                  GIMP_ITEM (mask)->height,
+                                  NULL, NULL, NULL, NULL))
     return;
 
   a = w / 2.0;
@@ -489,26 +486,24 @@ gimp_channel_combine_mask (GimpChannel    *mask,
 			   gint            off_y)
 {
   PixelRegion srcPR, destPR;
-  gint        x1, y1, x2, y2;
-  gint        w, h;
+  gint        x, y, w, h;
 
   g_return_if_fail (GIMP_IS_CHANNEL (mask));
   g_return_if_fail (GIMP_IS_CHANNEL (add_on));
 
-  x1 = CLAMP (off_x, 0, GIMP_ITEM (mask)->width);
-  y1 = CLAMP (off_y, 0, GIMP_ITEM (mask)->height);
-  x2 = CLAMP (off_x + GIMP_ITEM (add_on)->width, 0,
-	      GIMP_ITEM (mask)->width);
-  y2 = CLAMP (off_y + GIMP_ITEM (add_on)->height, 0,
-	      GIMP_ITEM (mask)->height);
-
-  w = (x2 - x1);
-  h = (y2 - y1);
+  if (! gimp_rectangle_intersect (off_x, off_y,
+                                  GIMP_ITEM (add_on)->width,
+                                  GIMP_ITEM (add_on)->height,
+                                  0, 0,
+                                  GIMP_ITEM (mask)->width,
+                                  GIMP_ITEM (mask)->height,
+                                  &x, &y, &w, &h))
+    return;
 
   pixel_region_init (&srcPR, GIMP_DRAWABLE (add_on)->tiles,
-		     (x1 - off_x), (y1 - off_y), w, h, FALSE);
+		     x - off_x, y - off_y, w, h, FALSE);
   pixel_region_init (&destPR, GIMP_DRAWABLE (mask)->tiles,
-                     x1, y1, w, h, TRUE);
+                     x, y, w, h, TRUE);
 
   switch (op)
     {
@@ -538,5 +533,5 @@ gimp_channel_combine_mask (GimpChannel    *mask,
 
   mask->bounds_known = FALSE;
 
-  gimp_drawable_update (GIMP_DRAWABLE (mask), x1, y2, w, h);
+  gimp_drawable_update (GIMP_DRAWABLE (mask), x, y, w, h);
 }