diff --git a/include/fmt/base.h b/include/fmt/base.h
index f407888e..b9fe4e8f 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -923,7 +923,7 @@ class locale_ref {
  public:
   constexpr locale_ref() : locale_(nullptr) {}
 
-  template <typename Locale, int = Locale::collate>
+  template <typename Locale, int = (Locale::collate, 0)>
   locale_ref(const Locale& loc) : locale_(&loc) {
     // Check if std::isalpha is found via ADL to reduce the chance of misuse.
     isalpha('x', loc);