--- a/memory/replace/logalloc/replay/Replay.cpp
+++ b/memory/replace/logalloc/replay/Replay.cpp
@@ -390,16 +390,19 @@ public:
     MemSlot& old_slot = (*this)[slot_id];
     void* old_ptr = old_slot.mPtr;
     old_slot.mPtr = nullptr;
     aSlot.mPtr = ::realloc_impl(old_ptr, size);
   }
 
   void free(Buffer& aArgs, Buffer& aResult)
   {
+    if (aResult) {
+      die("Malformed input");
+    }
     mOps++;
     Buffer dummy = aArgs.SplitChar('#');
     if (dummy) {
       die("Malformed input");
     }
     size_t slot_id = parseNumber(aArgs);
     MemSlot& slot = (*this)[slot_id];
     ::free_impl(slot.mPtr);
@@ -420,17 +423,17 @@ public:
     MemSlot& aSlot = SlotForResult(aResult);
     mOps++;
     size_t size = parseNumber(aArgs);
     aSlot.mPtr = ::valloc_impl(size);
   }
 
   void jemalloc_stats(Buffer& aArgs, Buffer& aResult)
   {
-    if (aArgs) {
+    if (aArgs || aResult) {
       die("Malformed input");
     }
     mOps++;
     jemalloc_stats_t stats;
     ::jemalloc_stats(&stats);
     FdPrintf(mStdErr,
              "#%zu mapped: %zu; allocated: %zu; waste: %zu; dirty: %zu; "
              "bookkeep: %zu; binunused: %zu\n", mOps, stats.mapped,