diff --git a/libc/bionic/semaphore.c b/libc/bionic/semaphore.c
index 0c94600..f4eebce 100644
--- a/libc/bionic/semaphore.c
+++ b/libc/bionic/semaphore.c
@@ -196,7 +196,8 @@
     if (__atomic_dec_if_positive(&sem->count) > 0) {
         return 0;
     } else {
-        return EAGAIN;
+        errno = EAGAIN;
+        return -1;
     }
 }