diff --git a/include/errno.h b/include/errno.h
index d9c2c9c7..9d680338 100644
--- a/include/errno.h
+++ b/include/errno.h
@@ -7,6 +7,9 @@ extern "C" {
 
 #include <bits/errno.h>
 
+#ifdef __GNUC__
+__attribute__((const))
+#endif
 extern int *__errno_location(void);
 #define errno (*__errno_location())
 
diff --git a/include/pthread.h b/include/pthread.h
index 5d97ebf6..a0af20fe 100644
--- a/include/pthread.h
+++ b/include/pthread.h
@@ -76,6 +76,9 @@ int pthread_detach(pthread_t);
 void pthread_exit(void *);
 int pthread_join(pthread_t, void **);
 
+#ifdef __GNUC__
+__attribute__((const))
+#endif
 pthread_t pthread_self(void);
 int pthread_equal(pthread_t, pthread_t);