diff --git a/include/jemalloc/internal/mutex_inlines.h b/include/jemalloc/internal/mutex_inlines.h
index 0c6c5dd5..c0c3cfe9 100644
--- a/include/jemalloc/internal/mutex_inlines.h
+++ b/include/jemalloc/internal/mutex_inlines.h
@@ -11,8 +11,8 @@ void	malloc_mutex_assert_not_owner(tsdn_t *tsdn, malloc_mutex_t *mutex);
 #if (defined(JEMALLOC_ENABLE_INLINE) || defined(JEMALLOC_MUTEX_C_))
 JEMALLOC_INLINE void
 malloc_mutex_lock(tsdn_t *tsdn, malloc_mutex_t *mutex) {
+	witness_assert_not_owner(tsdn, &mutex->witness);
 	if (isthreaded) {
-		witness_assert_not_owner(tsdn, &mutex->witness);
 #ifdef _WIN32
 #  if _WIN32_WINNT >= 0x0600
 		AcquireSRWLockExclusive(&mutex->lock);
@@ -26,14 +26,14 @@ malloc_mutex_lock(tsdn_t *tsdn, malloc_mutex_t *mutex) {
 #else
 		pthread_mutex_lock(&mutex->lock);
 #endif
-		witness_lock(tsdn, &mutex->witness);
 	}
+	witness_lock(tsdn, &mutex->witness);
 }
 
 JEMALLOC_INLINE void
 malloc_mutex_unlock(tsdn_t *tsdn, malloc_mutex_t *mutex) {
+	witness_unlock(tsdn, &mutex->witness);
 	if (isthreaded) {
-		witness_unlock(tsdn, &mutex->witness);
 #ifdef _WIN32
 #  if _WIN32_WINNT >= 0x0600
 		ReleaseSRWLockExclusive(&mutex->lock);
@@ -52,16 +52,12 @@ malloc_mutex_unlock(tsdn_t *tsdn, malloc_mutex_t *mutex) {
 
 JEMALLOC_INLINE void
 malloc_mutex_assert_owner(tsdn_t *tsdn, malloc_mutex_t *mutex) {
-	if (isthreaded) {
-		witness_assert_owner(tsdn, &mutex->witness);
-	}
+	witness_assert_owner(tsdn, &mutex->witness);
 }
 
 JEMALLOC_INLINE void
 malloc_mutex_assert_not_owner(tsdn_t *tsdn, malloc_mutex_t *mutex) {
-	if (isthreaded) {
-		witness_assert_not_owner(tsdn, &mutex->witness);
-	}
+	witness_assert_not_owner(tsdn, &mutex->witness);
 }
 #endif