diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 03b5dbd..d6fd62a 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -3455,6 +3455,11 @@
 {
     PyUnicodeObject *u;
 
+    if (str1->length == 0) {
+	PyErr_SetString(PyExc_ValueError, "empty pattern string");
+	return NULL;
+    }
+
     if (maxcount < 0)
 	maxcount = INT_MAX;