diff --git a/doc/examples/websocket.c b/doc/examples/websocket.c
index fad1e95f..4fa6f4ed 100644
--- a/doc/examples/websocket.c
+++ b/doc/examples/websocket.c
@@ -286,15 +286,16 @@ make_blocking (MHD_socket fd)
 
   flags = fcntl (fd, F_GETFL);
   if (-1 == flags)
-    return;
+    abort ();
   if ((flags & ~O_NONBLOCK) != flags)
     if (-1 == fcntl (fd, F_SETFL, flags & ~O_NONBLOCK))
       abort ();
-#else
+#else  /* _WIN32 */
   unsigned long flags = 0;
 
-  ioctlsocket (fd, FIONBIO, &flags);
-#endif
+  if (0 != ioctlsocket (fd, (int) FIONBIO, &flags))
+    abort ();
+#endif /* _WIN32 */
 }
 
 
diff --git a/src/examples/upgrade_example.c b/src/examples/upgrade_example.c
index b63d8802..93a2a72c 100644
--- a/src/examples/upgrade_example.c
+++ b/src/examples/upgrade_example.c
@@ -50,16 +50,16 @@ make_blocking (MHD_socket fd)
 
   flags = fcntl (fd, F_GETFL);
   if (-1 == flags)
-    return;
+    abort ();
   if ((flags & ~O_NONBLOCK) != flags)
     if (-1 == fcntl (fd, F_SETFL, flags & ~O_NONBLOCK))
       abort ();
 #elif defined(MHD_WINSOCK_SOCKETS)
   unsigned long flags = 0;
 
-  ioctlsocket (fd, (int) FIONBIO, &flags);
+  if (0 != ioctlsocket (fd, (int) FIONBIO, &flags))
+    abort ();
 #endif /* MHD_WINSOCK_SOCKETS */
-
 }
 
 
diff --git a/src/examples/websocket_chatserver_example.c b/src/examples/websocket_chatserver_example.c
index eb5dad39..70ad6cae 100644
--- a/src/examples/websocket_chatserver_example.c
+++ b/src/examples/websocket_chatserver_example.c
@@ -707,16 +707,16 @@ make_blocking (MHD_socket fd)
 
   flags = fcntl (fd, F_GETFL);
   if (-1 == flags)
-    return;
+    abort ();
   if ((flags & ~O_NONBLOCK) != flags)
     if (-1 == fcntl (fd, F_SETFL, flags & ~O_NONBLOCK))
       abort ();
 #elif defined(MHD_WINSOCK_SOCKETS)
   unsigned long flags = 0;
 
-  ioctlsocket (fd, FIONBIO, &flags);
+  if (0 != ioctlsocket (fd, (int) FIONBIO, &flags))
+    abort ();
 #endif /* MHD_WINSOCK_SOCKETS */
-
 }
 
 
diff --git a/src/examples/websocket_threaded_example.c b/src/examples/websocket_threaded_example.c
index 8680823f..3a232b41 100644
--- a/src/examples/websocket_threaded_example.c
+++ b/src/examples/websocket_threaded_example.c
@@ -519,14 +519,15 @@ make_blocking (MHD_socket fd)
 
   flags = fcntl (fd, F_GETFL);
   if (-1 == flags)
-    return;
+    abort ();
   if ((flags & ~O_NONBLOCK) != flags)
     if (-1 == fcntl (fd, F_SETFL, flags & ~O_NONBLOCK))
       abort ();
 #elif defined(MHD_WINSOCK_SOCKETS)
   unsigned long flags = 0;
 
-  ioctlsocket (fd, (int) FIONBIO, &flags);
+  if (0 != ioctlsocket (fd, (int) FIONBIO, &flags))
+    abort ();
 #endif /* MHD_WINSOCK_SOCKETS */
 }
 
diff --git a/src/microhttpd/test_upgrade.c b/src/microhttpd/test_upgrade.c
index b691bcda..873b832a 100644
--- a/src/microhttpd/test_upgrade.c
+++ b/src/microhttpd/test_upgrade.c
@@ -564,14 +564,15 @@ make_blocking (MHD_socket fd)
 
   flags = fcntl (fd, F_GETFL);
   if (-1 == flags)
-    return;
+    abort ();
   if ((flags & ~O_NONBLOCK) != flags)
     if (-1 == fcntl (fd, F_SETFL, flags & ~O_NONBLOCK))
       abort ();
 #elif defined(MHD_WINSOCK_SOCKETS)
   unsigned long flags = 0;
 
-  ioctlsocket (fd, (int) FIONBIO, &flags);
+  if (0 != ioctlsocket (fd, (int) FIONBIO, &flags))
+    abort ();
 #endif /* MHD_WINSOCK_SOCKETS */
 
 }
diff --git a/src/microhttpd/test_upgrade_large.c b/src/microhttpd/test_upgrade_large.c
index 6bbaf04d..e080266c 100644
--- a/src/microhttpd/test_upgrade_large.c
+++ b/src/microhttpd/test_upgrade_large.c
@@ -738,14 +738,15 @@ make_blocking (MHD_socket fd)
 
   flags = fcntl (fd, F_GETFL);
   if (-1 == flags)
-    return;
+    abort ();
   if ((flags & ~O_NONBLOCK) != flags)
     if (-1 == fcntl (fd, F_SETFL, flags & ~O_NONBLOCK))
       abort ();
 #elif defined(MHD_WINSOCK_SOCKETS)
   unsigned long flags = 0;
 
-  ioctlsocket (fd, (int) FIONBIO, &flags);
+  if (0 != ioctlsocket (fd, (int) FIONBIO, &flags))
+    abort ();
 #endif /* MHD_WINSOCK_SOCKETS */
 }