diff --git a/src/pthread/once.cpp b/src/pthread/once.cpp
index 2cfe7cd1..f61d74c8 100644
--- a/src/pthread/once.cpp
+++ b/src/pthread/once.cpp
@@ -15,7 +15,9 @@
 #include <pthread.h>
 #include <stdlib.h>
 #include <memory>
-
+#if defined BOOST_THREAD_PATCH
+#include <string.h> // memcmp.
+#endif
 namespace boost
 {
     namespace thread_detail
diff --git a/src/pthread/thread.cpp b/src/pthread/thread.cpp
index 730a43a6..aa29615d 100644
--- a/src/pthread/thread.cpp
+++ b/src/pthread/thread.cpp
@@ -126,7 +126,8 @@ namespace boost
                 }
                 ~delete_current_thread_tls_key_on_dlclose_t()
                 {
-                    if (current_thread_tls_init_flag.epoch!=BOOST_ONCE_INITIAL_FLAG_VALUE)
+                    const boost::once_flag uninitialized = BOOST_ONCE_INIT;
+                    if (memcmp(&current_thread_tls_init_flag, &uninitialized, sizeof(boost::once_flag)))
                     {
                         pthread_key_delete(current_thread_tls_key);
                     }