diff --git a/include/mutex b/include/mutex
index fbcc098..52e39b0 100644
--- a/include/mutex
+++ b/include/mutex
@@ -91,9 +91,9 @@
 struct try_to_lock_t {};
 struct adopt_lock_t {};
 
-constexpr defer_lock_t  defer_lock{};
-constexpr try_to_lock_t try_to_lock{};
-constexpr adopt_lock_t  adopt_lock{};
+inline constexpr defer_lock_t  defer_lock{};
+inline constexpr try_to_lock_t try_to_lock{};
+inline constexpr adopt_lock_t  adopt_lock{};
 
 template <class Mutex>
 class lock_guard