diff --git a/conservancy_beancount/errors.py b/conservancy_beancount/errors.py
index 7f331a49bfd5831759ed682009c185d58cd72e18..6d4611bbd9b1ad9cb4725b98acaf7a0cede9659f 100644
--- a/conservancy_beancount/errors.py
+++ b/conservancy_beancount/errors.py
@@ -65,3 +65,16 @@ class InvalidMetadataError(Error):
             txn,
             source,
         )
+
+
+class InvalidEntityError(InvalidMetadataError):
+    def __init__(self, txn, post=None, key='entity', value=None, source=None):
+        if post is None:
+            srcname = 'transaction'
+        else:
+            srcname = post.account
+        if value is None:
+            msg = "{} missing entity".format(srcname)
+        else:
+            msg = "{} entity malformed: {}".format(srcname, value)
+        super(InvalidMetadataError, self).__init__(msg, txn, source)