diff --git a/src/p_setup.c b/src/p_setup.c
index b8eae1c28..307d6969a 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -3334,7 +3334,7 @@ static void P_ProcessLinedefsAfterSidedefs(void)
 
 		if (ld->tripwire)
 		{
-			ld->blendmode = (subtractTripwire ? AST_SUBTRACT : AST_ADD);
+			ld->blendmode = (subtractTripwire ? AST_COPY : AST_ADD);
 			ld->alpha = FRACUNIT;
 		}