diff --git a/ChangeLog b/ChangeLog
index e497d8c2a..fb8d9203a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2005-07-16  Owen Taylor  <otaylor@redhat.com>
+
+        Patch from Martin Kretzschmar <martink@gnome.org>, #3798
+ 
+ 	* src/cairo-xlib-surface.c (_get_image_surface): prevent
+ 	sign-extension of masks.*_mask on 64bit architectures.
+ 	
+	* src/cairo-xcb-surface.c (_get_image_surface): ditto.
+	
 2005-07-28  Owen Taylor  <otaylor@redhat.com>
 
 	* src/cairo-image-surface.c (_cairo_image_surface_acquire_source,dest_image) 
diff --git a/src/cairo-xcb-surface.c b/src/cairo-xcb-surface.c
index 04f5892ed..b743cf4d8 100644
--- a/src/cairo-xcb-surface.c
+++ b/src/cairo-xcb-surface.c
@@ -481,10 +481,10 @@ _get_image_surface (cairo_xcb_surface_t    *surface,
 	masks.blue_mask = surface->visual->blue_mask;
     } else if (surface->has_format) {
 	masks.bpp = bpp;
-	masks.red_mask = surface->format.direct.red_mask << surface->format.direct.red_shift;
-	masks.green_mask = surface->format.direct.green_mask << surface->format.direct.green_shift;
-	masks.blue_mask = surface->format.direct.blue_mask << surface->format.direct.blue_shift;
-	masks.alpha_mask = surface->format.direct.alpha_mask << surface->format.direct.alpha_shift;
+	masks.red_mask = (unsigned long)surface->format.direct.red_mask << surface->format.direct.red_shift;
+	masks.green_mask = (unsigned long)surface->format.direct.green_mask << surface->format.direct.green_shift;
+	masks.blue_mask = (unsigned long)surface->format.direct.blue_mask << surface->format.direct.blue_shift;
+	masks.alpha_mask = (unsigned long)surface->format.direct.alpha_mask << surface->format.direct.alpha_shift;
     } else {
 	masks.bpp = bpp;
 	masks.red_mask = 0;
diff --git a/src/cairo-xlib-surface.c b/src/cairo-xlib-surface.c
index 39d101014..5f26a2f49 100644
--- a/src/cairo-xlib-surface.c
+++ b/src/cairo-xlib-surface.c
@@ -413,10 +413,10 @@ _get_image_surface (cairo_xlib_surface_t   *surface,
 	masks.blue_mask = surface->visual->blue_mask;
     } else if (surface->format) {
 	masks.bpp = ximage->bits_per_pixel;
-	masks.red_mask = surface->format->direct.redMask << surface->format->direct.red;
-	masks.green_mask = surface->format->direct.greenMask << surface->format->direct.green;
-	masks.blue_mask = surface->format->direct.blueMask << surface->format->direct.blue;
-	masks.alpha_mask = surface->format->direct.alphaMask << surface->format->direct.alpha;
+	masks.red_mask = (unsigned long)surface->format->direct.redMask << surface->format->direct.red;
+	masks.green_mask = (unsigned long)surface->format->direct.greenMask << surface->format->direct.green;
+	masks.blue_mask = (unsigned long)surface->format->direct.blueMask << surface->format->direct.blue;
+	masks.alpha_mask = (unsigned long)surface->format->direct.alphaMask << surface->format->direct.alpha;
     } else {
 	masks.bpp = ximage->bits_per_pixel;
 	masks.red_mask = 0;