diff --git a/ssl/test/handshake_util.cc b/ssl/test/handshake_util.cc
index 62fbbf7..f839653 100644
--- a/ssl/test/handshake_util.cc
+++ b/ssl/test/handshake_util.cc
@@ -345,7 +345,9 @@
       return false;
   }
 
-  pid_t handshaker_pid;
+  // MSan doesn't know that |posix_spawn| initializes its output, so initialize
+  // it to -1.
+  pid_t handshaker_pid = -1;
   int ret = posix_spawn(&handshaker_pid, args[0], &actions, nullptr,
                         args.data(), nullptr);
   if (posix_spawn_file_actions_destroy(&actions) != 0 ||