diff --git a/common/polylib.c b/common/polylib.c
index 4125ab0a..96120af5 100644
--- a/common/polylib.c
+++ b/common/polylib.c
@@ -72,8 +72,8 @@ WindingPlane(const winding_t * w, vec3_t normal, vec_t *dist)
 {
     vec3_t v1, v2;
 
-    VectorSubtract(w->p[1], w->p[0], v1);
-    VectorSubtract(w->p[2], w->p[0], v2);
+    VectorSubtract(w->p[0], w->p[1], v1);
+    VectorSubtract(w->p[2], w->p[1], v2);
     CrossProduct(v1, v2, normal);
     VectorNormalize(normal);
     *dist = DotProduct(w->p[0], normal);