diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index cf4f842..24eda6b 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -4896,7 +4896,7 @@
 #if SIZEOF_WCHAR_T == 4
             assert(0);
 #else
-            assert(Py_UNICODE_IS_SURROGATE(ch));
+            assert(ch > 0xFFFF && ch <= MAX_UNICODE);
             /*  compute and append the two surrogates: */
             unicode[outpos++] = (wchar_t)Py_UNICODE_HIGH_SURROGATE(ch);
             unicode[outpos++] = (wchar_t)Py_UNICODE_LOW_SURROGATE(ch);