diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 9ab366d..ab4559f 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -1652,7 +1652,7 @@
     case PyUnicode_1BYTE_KIND: {
         Py_ssize_t len = strlen(str);
         assert(index + len <= PyUnicode_GET_LENGTH(unicode));
-        memcpy(data + index, str, len);
+        memcpy((char *) data + index, str, len);
         return len;
     }
     case PyUnicode_2BYTE_KIND: {