diff --git a/zipline/assets/asset_db_schema.py b/zipline/assets/asset_db_schema.py
index 19660e90..29f6b568 100644
--- a/zipline/assets/asset_db_schema.py
+++ b/zipline/assets/asset_db_schema.py
@@ -1,7 +1,14 @@
 import sqlalchemy as sa
 
 
+# Define a version number for the database generated by these writers
+# Increment this version number any time a change is made to the schema of the
+# assets database
+ASSET_DB_VERSION = 0
+
+
 def generate_asset_db_metadata(bind=None):
+    # NOTE: When modifying this schema, update the ASSET_DB_VERSION value
     metadata = sa.MetaData(bind=bind)
     _version_table_schema(metadata)
     _equities_table_schema(metadata)
@@ -12,19 +19,15 @@ def generate_asset_db_metadata(bind=None):
     return metadata
 
 
-# Define a version number for the database generated by these writers
-# Increment this version number any time a breaking change is made to the
-# schema and readers of the database
-ASSET_DB_VERSION = 0
-
-
 # A list of the names of all tables in the assets db
+# NOTE: When modifying this schema, update the ASSET_DB_VERSION value
 asset_db_table_names = ['version_info', 'equities', 'futures_exchanges',
                         'futures_root_symbols', 'futures_contracts',
                         'asset_router']
 
 
 def _equities_table_schema(metadata):
+    # NOTE: When modifying this schema, update the ASSET_DB_VERSION value
     return sa.Table(
         'equities',
         metadata,
@@ -48,6 +51,7 @@ def _equities_table_schema(metadata):
 
 
 def _futures_exchanges_schema(metadata):
+    # NOTE: When modifying this schema, update the ASSET_DB_VERSION value
     return sa.Table(
         'futures_exchanges',
         metadata,
@@ -63,6 +67,7 @@ def _futures_exchanges_schema(metadata):
 
 
 def _futures_root_symbols_schema(metadata):
+    # NOTE: When modifying this schema, update the ASSET_DB_VERSION value
     return sa.Table(
         'futures_root_symbols',
         metadata,
@@ -85,6 +90,7 @@ def _futures_root_symbols_schema(metadata):
 
 
 def _futures_contracts_schema(metadata):
+    # NOTE: When modifying this schema, update the ASSET_DB_VERSION value
     return sa.Table(
         'futures_contracts',
         metadata,
@@ -119,6 +125,7 @@ def _futures_contracts_schema(metadata):
 
 
 def _asset_router_schema(metadata):
+    # NOTE: When modifying this schema, update the ASSET_DB_VERSION value
     return sa.Table(
         'asset_router',
         metadata,
@@ -133,6 +140,7 @@ def _asset_router_schema(metadata):
 
 
 def _version_table_schema(metadata):
+    # NOTE: When modifying this schema, update the ASSET_DB_VERSION value
     return sa.Table(
         'version_info',
         metadata,