diff --git a/vm/Makefile b/vm/Makefile
index 061c10f..a48a032 100644
--- a/vm/Makefile
+++ b/vm/Makefile
@@ -6,7 +6,7 @@
 verbose ?= yes
 OBJDIR = ob
 
-FLAGS=-O2 -Wall -fno-builtin-log -I. -Werror=implicit-function-declaration -Werror
+FLAGS=-O2 -Wall -Wextra -Wno-unused-parameter -fno-builtin-log -I. -Werror=implicit-function-declaration -Werror
 
 dv_src = $(shell ls dv/*.c)
 in_src = $(shell ls in/*.c)
diff --git a/vm/in/mem.c b/vm/in/mem.c
index 36fed68..ed97fca 100644
--- a/vm/in/mem.c
+++ b/vm/in/mem.c
@@ -174,7 +174,7 @@ IMPL_START(enter, 1)
 
 IMPL_START(enter, 2)
 {
-    int i, tmp;
+    ulong i, tmp;
 
     R(ESP) -= 8;
     tmp = R(ESP);