diff --git a/tests/string_test.cpp b/tests/string_test.cpp
index 30c87dc..38957e2 100644
--- a/tests/string_test.cpp
+++ b/tests/string_test.cpp
@@ -136,7 +136,7 @@
   // A real-time signal.
   ASSERT_STREQ("Real-time signal 14", strsignal(SIGRTMIN + 14));
   // One of the signals the C library keeps to itself.
-  ASSERT_STREQ("Unknown signal 32", strsignal(__SIGRTMIN));
+  ASSERT_STREQ("Unknown signal 32", strsignal(32));  // __SIGRTMIN
 
   // Errors.
   ASSERT_STREQ("Unknown signal -1", strsignal(-1)); // Too small.