diff --git a/Makefile b/Makefile
index 39f775f961..0a9ad4795f 100644
--- a/Makefile
+++ b/Makefile
@@ -238,7 +238,7 @@ ifeq ($(AST_DEVMODE),yes)
 endif
 
 ifneq ($(findstring BSD,$(OSARCH)),)
-  _ASTCFLAGS+=-I/usr/local/include
+  _ASTCFLAGS+=-isystem /usr/local/include
 endif
 
 ifneq ($(PROC),ultrasparc)