diff --git a/vm.c b/vm.c
index 82804225..83cd44cf 100644
--- a/vm.c
+++ b/vm.c
@@ -1506,6 +1506,9 @@ sexp sexp_apply (sexp ctx, sexp proc, sexp args) {
     _ALIGN_IP();
     sexp_context_top(ctx) = top;
     _PUSH(sexp_alloc_tagged(ctx, _UWORD1, _UWORD0));
+    /* initialize fields to void */
+    for (i=(_UWORD1-sexp_sizeof_header)/sizeof(sexp_uint_t) - 1; i>=0; i--)
+      sexp_slot_set(_ARG1, i, SEXP_VOID);
     ip += sizeof(sexp)*2;
     break;
   case SEXP_OP_SLOT_REF: