1 files changed, 6 insertions, 1 deletions
diff --git a/win32/win32.c b/win32/win32.c
index 72ca08f55e..a4cea9b287 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -1811,7 +1811,12 @@ rb_w32_fdclr(int fd, fd_set *set)
 int
 rb_w32_fdisset(int fd, fd_set *set)
 {
-    return __WSAFDIsSet(TO_SOCKET(fd), set);
+    int ret;
+    SOCKET s = TO_SOCKET(fd);
+    if (s == (SOCKET)INVALID_HANDLE_VALUE)
+        return 0;
+    RUBY_CRITICAL(ret = __WSAFDIsSet(s, set));
+    return ret;
 }
 
 //