diff --git a/webcc/logger.cc b/webcc/logger.cc
index 42a2b48..243039d 100644
--- a/webcc/logger.cc
+++ b/webcc/logger.cc
@@ -16,7 +16,8 @@
 #include <Windows.h>
 #else
 // For getting thread ID.
-#include <sys/syscall.h>
+#include <unistd.h>
+#include <sys/syscall.h>  // For SYS_xxx definitions
 #include <sys/types.h>
 #endif  // defined(_WIN32) || defined(_WIN64)