diff --git a/src/cairo-image-surface.c b/src/cairo-image-surface.c
index 3de056882..4aad77f05 100644
--- a/src/cairo-image-surface.c
+++ b/src/cairo-image-surface.c
@@ -572,8 +572,6 @@ cairo_image_surface_get_format (cairo_surface_t *surface)
 	return 0;
     }
 
-    assert (CAIRO_FORMAT_VALID (image_surface->format));
-
     return image_surface->format;
 }