diff --git a/indra/develop.py b/indra/develop.py
index b8fdd1a81507726073f28e8a3c1c5b2ea26ab883..59722c4bc2e2ba0ef3e0fb5a57f5539b294c5538 100755
--- a/indra/develop.py
+++ b/indra/develop.py
@@ -630,6 +630,8 @@ def run_vstool(self):
             print >> open(stamp, 'w'), self.build_type
         
     def run_build(self, opts, targets):
+        for t in targets:
+            assert t.strip(), 'Unexpected empty targets: ' + repr(targets)
         cwd = getcwd()
         executable, build_cmd = self.get_build_cmd()