diff --git a/src/test/sock_tests.cpp b/src/test/sock_tests.cpp
index cc0e6e70575..ed9780dfb53 100644
--- a/src/test/sock_tests.cpp
+++ b/src/test/sock_tests.cpp
@@ -95,7 +95,7 @@ static void CreateSocketPair(int s[2])
 static void SendAndRecvMessage(const Sock& sender, const Sock& receiver)
 {
     const char* msg = "abcd";
-    constexpr size_t msg_len = 4;
+    constexpr ssize_t msg_len = 4;
     char recv_buf[10];
 
     BOOST_CHECK_EQUAL(sender.Send(msg, msg_len, 0), msg_len);