--- a/parser/python_header.h
+++ b/parser/python_header.h
@@ -13,6 +13,7 @@
 
 #include <language/duchain/duchainlock.h>
 
+#include <sys/types.h> /* define ssize_t with musl libc */
 #include "pyport.h"
 #ifndef _WIN32
 #include "pyconfig.h"