diff --git a/dtool/src/dtoolbase/mutexPosixImpl.I b/dtool/src/dtoolbase/mutexPosixImpl.I
index 0bc338a2eb..dabc432cbd 100644
--- a/dtool/src/dtoolbase/mutexPosixImpl.I
+++ b/dtool/src/dtoolbase/mutexPosixImpl.I
@@ -15,7 +15,7 @@
  *
  */
 constexpr MutexPosixImpl::
-MutexPosixImpl() noexcept : _lock(PTHREAD_MUTEX_INITIALIZER) {
+MutexPosixImpl() noexcept {
 }
 
 /**
diff --git a/dtool/src/dtoolbase/mutexPosixImpl.h b/dtool/src/dtoolbase/mutexPosixImpl.h
index 996001b114..c5509d1064 100644
--- a/dtool/src/dtoolbase/mutexPosixImpl.h
+++ b/dtool/src/dtoolbase/mutexPosixImpl.h
@@ -40,7 +40,7 @@ public:
   INLINE void unlock();
 
 private:
-  pthread_mutex_t _lock;
+  pthread_mutex_t _lock = PTHREAD_MUTEX_INITIALIZER;
   friend class ConditionVarPosixImpl;
 };