diff --git a/ognibuild/buildsystem.py b/ognibuild/buildsystem.py
index e351d0b..cd2e010 100644
--- a/ognibuild/buildsystem.py
+++ b/ognibuild/buildsystem.py
@@ -524,7 +524,8 @@ class R(BuildSystem):
 
     @classmethod
     def probe(cls, path):
-        if os.path.exists(os.path.join(path, 'DESCRIPTION')):
+        if (os.path.exists(os.path.join(path, 'DESCRIPTION')) and
+                os.path.exists(os.path.join(path, 'NAMESPACE'))):
             return cls(path)
 
     def _read_description(self):