1 files changed, 4 insertions, 1 deletions
diff --git a/win32/win32.c b/win32/win32.c
index 1a859a5a3f..53f8dc9c25 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -1811,7 +1811,10 @@ rb_w32_fdclr(int fd, fd_set *set)
 int
 rb_w32_fdisset(int fd, fd_set *set)
 {
-       return __WSAFDIsSet(TO_SOCKET(fd), set);
+    SOCKET s = TO_SOCKET(fd);
+    if (!is_socket(s))
+        return 0;
+    return __WSAFDIsSet(s, set);
 }
 
 //