diff --git a/ExplorerPatcher/utility.h b/ExplorerPatcher/utility.h
index a8bcdec..77203d6 100644
--- a/ExplorerPatcher/utility.h
+++ b/ExplorerPatcher/utility.h
@@ -268,7 +268,7 @@ static inline WCHAR* rand_string(WCHAR* str, size_t size)
     if (size) {
         --size;
         for (size_t n = 0; n < size; n++) {
-            int key = rand() % (int)(sizeof charset - 1);
+            int key = rand() % (int)((sizeof(charset) / sizeof(WCHAR)) - 1);
             str[n] = charset[key];
         }
         str[size] = L'\0';