diff --git a/Objects/stringlib/fastsearch.h b/Objects/stringlib/fastsearch.h
index b447865c986bef..26bb0555ca9b6c 100644
--- a/Objects/stringlib/fastsearch.h
+++ b/Objects/stringlib/fastsearch.h
@@ -69,8 +69,8 @@ STRINGLIB(find_char)(const STRINGLIB_CHAR* s, Py_ssize_t n, STRINGLIB_CHAR ch)
            and UCS4 representations. */
         if (needle != 0) {
             do {
-                void *candidate = memchr(p, needle,
-                                         (e - p) * sizeof(STRINGLIB_CHAR));
+                const void *candidate = memchr(p, needle,
+                                               (e - p) * sizeof(STRINGLIB_CHAR));
                 if (candidate == NULL)
                     return -1;
                 s1 = p;