diff --git a/project.py b/project.py
index b81fcd5f0..36039321f 100644
--- a/project.py
+++ b/project.py
@@ -4398,8 +4398,12 @@ class Project:
                 except AttributeError:
                     pass
                 if line.startswith("ref: "):
-                    return line[5:-1]
-                return line[:-1]
+                    ref = line[5:-1]
+                else:
+                    ref = line[:-1]
+                if ref == R_HEADS + ".invalid":
+                    raise NoManifestException(path, str(e))
+                return ref
 
         def SetHead(self, ref, message=None):
             cmdv = []