diff --git a/chrome/browser/extensions/extension_process_manager.cc b/chrome/browser/extensions/extension_process_manager.cc
index 57b969bd27cc9c2fd5525811027752790a6d72d0..0a362a487c533e85682adac12771478eb5bd808e 100644
--- a/chrome/browser/extensions/extension_process_manager.cc
+++ b/chrome/browser/extensions/extension_process_manager.cc
@@ -90,6 +90,9 @@ void ExtensionProcessManager::RegisterExtensionProcess(
   if (it != process_ids_.end() && (*it).second == process_id)
     return;
 
+  // Extension ids should get removed from the map before the process ids get
+  // reused from a dead renderer.
+  DCHECK(it == process_ids_.end());
   process_ids_[extension_id] = process_id;
 
   ExtensionsService* extension_service =