diff --git a/code_annotations/contrib/sphinx/extensions/openedx_events.py b/code_annotations/contrib/sphinx/extensions/openedx_events.py
index 9a9f05d..99e695d 100644
--- a/code_annotations/contrib/sphinx/extensions/openedx_events.py
+++ b/code_annotations/contrib/sphinx/extensions/openedx_events.py
@@ -87,7 +87,7 @@ def iter_nodes(self):
             event_name = event[".. event_name:"]
             event_name_literal = nodes.literal(text=quote_value(event_name))
             event_data = event[".. event_data:"]
-            event_key_field = event.get(".. event_key_field:", None)
+            event_key_field = event.get(".. event_key_field:", "")
             event_key_literal = nodes.literal(text=quote_value(event_key_field))
             event_description = event[".. event_description:"]
 
@@ -103,11 +103,16 @@ def iter_nodes(self):
             event_section += nodes.paragraph(text=f"Description:"
                                                   f" {event_description}")
             event_section += nodes.paragraph(text=f"Event data: {event_data}")
-            event_section += nodes.paragraph(
-                text=f"Defined at: {event['filename']} (line"
-                     f" {event['line_number']})"
+            source = nodes.reference(
+                text=f"{event['filename']} (line {event['line_number']})",
+                refuri="{}/blob/{}/{}#L{}".format(
+                    self.env.config.openedxevents_repo_url,
+                    self.env.config.openedxevents_repo_version,
+                    event['filename'],
+                    event['line_number'],
+                ),
             )
-
+            event_section += nodes.paragraph("", "Defined at:", source)
             domain_header += event_section
 
         if domain_header: