diff --git a/include/cmocka.h b/include/cmocka.h
index bfcdd3f..60467b9 100644
--- a/include/cmocka.h
+++ b/include/cmocka.h
@@ -56,7 +56,7 @@ int __stdcall IsDebuggerPresent();
 
 /* If __WORDSIZE is not set, try to figure it out and default to 32 bit. */
 #ifndef __WORDSIZE
-# if defined(__x86_64__) && !defined(__ILP32__)
+# if ( defined(__x86_64__) && !defined(__ILP32__) ) || defined(__s390x__)
 #  define __WORDSIZE 64
 # else
 #  define __WORDSIZE 32