diff --git a/py/gc.c b/py/gc.c
index 24d8e1a..8e71307 100644
--- a/py/gc.c
+++ b/py/gc.c
@@ -484,7 +484,11 @@
             #if EXTENSIVE_HEAP_PROFILING
             gc_dump_alloc_table();
             #endif
+        } else {
+            assert(!"bad free");
         }
+    } else if (ptr_in != NULL) {
+        assert(!"bad free");
     }
 }