diff --git a/Tools/ardupilotwaf/ardupilotwaf.py b/Tools/ardupilotwaf/ardupilotwaf.py
index eb7452f1c9..dd66b19c58 100644
--- a/Tools/ardupilotwaf/ardupilotwaf.py
+++ b/Tools/ardupilotwaf/ardupilotwaf.py
@@ -380,7 +380,7 @@ def ap_version_append_str(ctx, k, v):
 
 @conf
 def ap_version_append_int(ctx, k, v):
-    ctx.env['AP_VERSION_ITEMS'] += [(k,v)]
+    ctx.env['AP_VERSION_ITEMS'] += [(k, '{}'.format(os.environ.get(k, v)))]
 
 @conf
 def write_version_header(ctx, tgt):