diff --git a/racket/src/foreign/foreign.c b/racket/src/foreign/foreign.c
index 7260597b7d..2a446785c6 100644
--- a/racket/src/foreign/foreign.c
+++ b/racket/src/foreign/foreign.c
@@ -3929,7 +3929,7 @@ static Scheme_Object *foreign_ffi_callback(int argc, Scheme_Object *argv[])
        `free_cl_cif_queue_args' to clean up this extra level. */
     GC_CAN_IGNORE void **tmp, *cr;
     if (constant_reply) {
-      cr = malloc(constant_reply_size);
+      cr = malloc(constant_reply_size ? constant_reply_size : 1);
       memcpy(cr, constant_reply, constant_reply_size);
       constant_reply = cr;
     }
diff --git a/racket/src/foreign/foreign.rktc b/racket/src/foreign/foreign.rktc
index 457fd4985c..da8074964d 100755
--- a/racket/src/foreign/foreign.rktc
+++ b/racket/src/foreign/foreign.rktc
@@ -3127,7 +3127,7 @@ static void free_cl_cif_queue_args(void *ignored, void *p)
          `free_cl_cif_queue_args' to clean up this extra level. */
       GC_CAN_IGNORE void **tmp, *cr;
       if (constant_reply) {
-        cr = malloc(constant_reply_size);
+        cr = malloc(constant_reply_size ? constant_reply_size : 1);
         memcpy(cr, constant_reply, constant_reply_size);
         constant_reply = cr;
       }