diff --git a/.github/workflows/doctor.yml b/.github/workflows/doctor.yml
index 03b94063fe..c7baad301f 100644
--- a/.github/workflows/doctor.yml
+++ b/.github/workflows/doctor.yml
@@ -1,6 +1,6 @@
 name: brew doctor
 on:
-  push:
+  pull_request:
     paths:
       - .github/workflows/doctor.yml
       - Library/Homebrew/cmd/doctor.rb
diff --git a/Library/Homebrew/tab.rb b/Library/Homebrew/tab.rb
index 96386c728e..8283d08cb0 100644
--- a/Library/Homebrew/tab.rb
+++ b/Library/Homebrew/tab.rb
@@ -324,7 +324,7 @@ class Tab < OpenStruct
   end
 
   def source_modified_time
-    Time.at(super)
+    Time.at(super || 0)
   end
 
   def to_json(options = nil)