diff --git a/lib/pthread_sigmask.c b/lib/pthread_sigmask.c
index 3bb92ca8e..ff0a514f0 100644
--- a/lib/pthread_sigmask.c
+++ b/lib/pthread_sigmask.c
@@ -30,6 +30,7 @@
 # include <unistd.h>
 #endif
 
+#if defined pthread_sigmask && pthread_sigmask != 0
 int
 pthread_sigmask (int how, const sigset_t *new_mask, sigset_t *old_mask)
 #undef pthread_sigmask
@@ -90,3 +91,4 @@ pthread_sigmask (int how, const sigset_t *new_mask, sigset_t *old_mask)
   return (ret < 0 ? errno : 0);
 #endif
 }
+#endif