diff --git a/sample_mm/Makefile b/sample_mm/Makefile
index c2e0d92..158186e 100755
--- a/sample_mm/Makefile
+++ b/sample_mm/Makefile
@@ -38,6 +38,10 @@ ifeq "$(ENGINE)" "orangebox"
 	INCLUDE += -I$(HL2SDK)/public/game/server
 	SRCDS = $(SRCDS_BASE)/orangebox
 endif
+ifeq "$(ENGINE)" ""
+	echo "You must supply ENGINE=orangebox or ENGINE=original"
+	false
+endif
 
 LINK += $(HL2SDK)/linux_sdk/tier1_i486.a vstdlib_i486.so tier0_i486.so
 
diff --git a/sample_mm/sample_mm.cpp b/sample_mm/sample_mm.cpp
index 0ca544c..c72f7ea 100644
--- a/sample_mm/sample_mm.cpp
+++ b/sample_mm/sample_mm.cpp
@@ -166,7 +166,7 @@ void StubPlugin::Hook_ClientCommand(edict_t *pEntity)
 	CCommand args;
 #endif
 
-	if (!pEntity || !pEntity->IsFree())
+	if (!pEntity || pEntity->IsFree())
 	{
 		return;
 	}
diff --git a/stub_mm/Makefile b/stub_mm/Makefile
index 0573891..c96e914 100644
--- a/stub_mm/Makefile
+++ b/stub_mm/Makefile
@@ -35,9 +35,13 @@ ifeq "$(ENGINE)" "orangebox"
 	HL2PUB = $(HL2SDK_OB)/public
 	CFLAGS += -DENGINE_ORANGEBOX
 	METAMOD = $(SOURCEMM16)
-	INCLUDE += -I$(HL2SDK)/game/server
+	INCLUDE += -I$(HL2SDK)/public/game/server
 	SRCDS = $(SRCDS_BASE)/orangebox
 endif
+ifeq "$(ENGINE)" ""
+	echo "You must supply ENGINE=orangebox or ENGINE=original"
+	false
+endif
 
 LINK += $(HL2SDK)/linux_sdk/tier1_i486.a vstdlib_i486.so tier0_i486.so