diff --git a/pixman/pixman.h b/pixman/pixman.h
index 7ff9fb5..ddcce13 100644
--- a/pixman/pixman.h
+++ b/pixman/pixman.h
@@ -1030,7 +1030,7 @@ struct pixman_triangle
 #define pixman_trapezoid_valid(t)				   \
     ((t)->left.p1.y != (t)->left.p2.y &&			   \
      (t)->right.p1.y != (t)->right.p2.y &&			   \
-     (int) ((t)->bottom - (t)->top) > 0)
+     (t)->bottom > 0 && (int) ((t)->bottom - (t)->top) > 0)
 
 struct pixman_span_fix
 {