diff --git a/dlls/ws2_32/tests/sock.c b/dlls/ws2_32/tests/sock.c
index 98cc3881853..2b0a7354f4b 100644
--- a/dlls/ws2_32/tests/sock.c
+++ b/dlls/ws2_32/tests/sock.c
@@ -10530,7 +10530,7 @@ static void test_wsaioctl(void)
     ok(size && size != 0xdeadbeef && !(size % sizeof(INTERFACE_INFO)), "Got unexpected size %u.\n", size);
 
     size = 0xdeadbeef;
-    ret = WSAIoctl(s, SIO_GET_INTERFACE_LIST, NULL, 0, buffer, sizeof(INTERFACE_INFO), &size, NULL, NULL);
+    ret = WSAIoctl(s, SIO_GET_INTERFACE_LIST, NULL, 0, buffer, sizeof(INTERFACE_INFO) - 1, &size, NULL, NULL);
     ok(ret == -1, "Got unexpected ret %d.\n", ret);
     ok(WSAGetLastError() == WSAEFAULT, "Got unexpected error %d.\n", WSAGetLastError());
     ok(!size, "Got unexpected size %u.\n", size);