diff --git a/compose/project.py b/compose/project.py
index d965c4a39..1b7fde23b 100644
--- a/compose/project.py
+++ b/compose/project.py
@@ -539,4 +539,5 @@ class NoSuchService(Exception):
 
 
 class ProjectError(Exception):
-    pass
+    def __init__(self, msg):
+        self.msg = msg