diff --git a/include/fmt/base.h b/include/fmt/base.h
index d7679757..e58a5d72 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -924,7 +924,10 @@ class locale_ref {
   constexpr locale_ref() : locale_(nullptr) {}
 
   template <typename Locale, FMT_ENABLE_IF(sizeof(Locale::collate) != 0)>
-  locale_ref(const Locale& loc);
+  locale_ref(const Locale& loc) : locale_(&loc) {
+    // Check if std::isalpha is found via ADL to reduce the chance of misuse.
+    isalpha('x', loc);
+  }
 
   inline explicit operator bool() const noexcept { return locale_ != nullptr; }
 #endif  // FMT_USE_LOCALE
diff --git a/src/format.cc b/src/format.cc
index 05d0105b..e583446e 100644
--- a/src/format.cc
+++ b/src/format.cc
@@ -10,7 +10,7 @@
 FMT_BEGIN_NAMESPACE
 
 #if FMT_USE_LOCALE
-template FMT_API locale_ref::locale_ref(const std::locale& loc);
+template FMT_API locale_ref::locale_ref(const std::locale& loc); // DEPRECATED!
 template FMT_API auto locale_ref::get<std::locale>() const -> std::locale;
 #endif