diff --git a/core/Makefile b/core/Makefile
index 2d1e598d..4799c5e9 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -76,7 +76,7 @@ ifeq "$(ENGINE)" "orangeboxvalve"
 	HL2LIB = $(HL2SDK)/lib/linux
 	CFLAGS += -DSOURCE_ENGINE=4
 	METAMOD = $(MMSOURCE17)/core
-	INCLUDE += -I$(HL2SDK)/public/game/server
+	INCLUDE += -I$(HL2SDK)/public/game/server -I$(HL2SDK)/common
 	SRCDS = $(SRCDS_BASE)/orangebox
 	BINARY = sourcemod.2.ep2valve.so
 	override ENGSET = true