diff --git a/src/vm.c b/src/vm.c
index 225d007c1..aaf1fbb77 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -102,7 +102,9 @@ stack_clear(mrb_value *from, size_t count)
 static inline void
 stack_copy(mrb_value *dst, const mrb_value *src, size_t size)
 {
-  memcpy(dst, src, sizeof(mrb_value)*size);
+  if (src) {
+    memcpy(dst, src, sizeof(mrb_value)*size);
+  }
 }
 
 static void