diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 157ea1c..e227fc7 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -1204,7 +1204,10 @@
 char*
 PyUnicode_AsString(PyObject *unicode)
 {
-    assert(PyUnicode_Check(unicode));
+    if (!PyUnicode_Check(unicode)) {
+        PyErr_BadArgument();
+        return NULL;
+    }
     unicode = _PyUnicode_AsDefaultEncodedString(unicode, NULL);
     if (!unicode)
         return NULL;