diff --git a/core/vm.c b/core/vm.c
index 4f083b93..a8ad721f 100644
--- a/core/vm.c
+++ b/core/vm.c
@@ -254,6 +254,8 @@ PN potion_vm(Potion *P, PN proto, PN self, PN vargs, PN_SIZE upc, PN *upargs) {
 
   if (pos == 0) {
     reg[-1] = reg[0] = self;
+    if (f->localsize)
+      memset((void*)locals, 0, sizeof(*locals) * f->localsize);
     if (upc > 0 && upargs != NULL) {
       PN_SIZE i;
       for (i = 0; i < upc; i++) {