diff --git a/src/glamor_trapezoid.c b/src/glamor_trapezoid.c
index 57a178c..f318f4b 100644
--- a/src/glamor_trapezoid.c
+++ b/src/glamor_trapezoid.c
@@ -855,7 +855,7 @@ _glamor_trapezoids_with_shader(CARD8 op,
 			mclip_rect = 1;
 			ptrap = traps;
 			traps_count = ntriangle_per_loop / 4;
-			traps_not_completed = ntrap - traps_count;
+			traps_not_completed = nclip_rect * ntrap - traps_count;
 		} else {
 			traps_count = ntrap;
 			ptrap = traps;