# HG changeset patch
# Parent 5c306845e67c7e136b9c03e537838d99ad4ab175

diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -1917,8 +1917,10 @@ cmsg_min_space(struct msghdr *msg, struc
     static const size_t cmsg_len_end = (offsetof(struct cmsghdr, cmsg_len) +
                                         sizeof(cmsgh->cmsg_len));
 
-    /* Note that POSIX allows msg_controllen to be of signed type. */
-    if (cmsgh == NULL || msg->msg_control == NULL || msg->msg_controllen < 0)
+    /* Note that POSIX allows msg_controllen to be of signed type, in
+       which case we need the comparison to be signed. */
+    if (cmsgh == NULL || msg->msg_control == NULL ||
+        msg->msg_controllen < (Py_ssize_t)cmsg_len_end)
         return 0;
     if (space < cmsg_len_end)
         space = cmsg_len_end;