diff --git a/src/portal.cpp b/src/portal.cpp
index f180a4fbfa..bf919f09a4 100644
--- a/src/portal.cpp
+++ b/src/portal.cpp
@@ -288,7 +288,7 @@ static void SetRotation(FLinePortal *port)
 			}
 			else
 			{
-				port->mFlags &= PORTF_POLYOBJ;
+				port->mFlags &= ~PORTF_POLYOBJ;
 			}
 		}
 		else