1 files changed, 18 insertions, 1 deletions
diff --git a/python/google/protobuf/descriptor_database.py b/python/google/protobuf/descriptor_database.py
index 8665d3c5..9f5a117c 100644
--- a/python/google/protobuf/descriptor_database.py
+++ b/python/google/protobuf/descriptor_database.py
@@ -33,6 +33,14 @@
 __author__ = 'matthewtoia@google.com (Matt Toia)'
 
 
+class Error(Exception):
+  pass
+
+
+class DescriptorDatabaseConflictingDefinitionError(Error):
+  """Raised when a proto is added with the same name & different descriptor."""
+
+
 class DescriptorDatabase(object):
   """A container accepting FileDescriptorProtos and maps DescriptorProtos."""
 
@@ -45,9 +53,18 @@ class DescriptorDatabase(object):
 
     Args:
       file_desc_proto: The FileDescriptorProto to add.
+    Raises:
+      DescriptorDatabaseException: if an attempt is made to add a proto
+        with the same name but different definition than an exisiting
+        proto in the database.
     """
+    proto_name = file_desc_proto.name
+    if proto_name not in self._file_desc_protos_by_file:
+      self._file_desc_protos_by_file[proto_name] = file_desc_proto
+    elif self._file_desc_protos_by_file[proto_name] != file_desc_proto:
+      raise DescriptorDatabaseConflictingDefinitionError(
+          '%s already added, but with different descriptor.' % proto_name)
 
-    self._file_desc_protos_by_file[file_desc_proto.name] = file_desc_proto
     package = file_desc_proto.package
     for message in file_desc_proto.message_type:
       self._file_desc_protos_by_symbol.update(