diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index 4cc59daa60..417aee51ac 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -695,18 +695,31 @@ class BazaarDownloadStrategy < AbstractDownloadStrategy
       ].find { |p| File.executable? p }
   end
 
+  def repo_valid?
+    @clone.join(".bzr").directory?
+  end
+
   def fetch
     ohai "Cloning #{@url}"
-    unless @clone.exist?
-      url=@url.sub(%r[^bzr://], '')
-      # 'lightweight' means history-less
-      safe_system bzrpath, 'checkout', '--lightweight', url, @clone
-    else
+
+    if @clone.exist? && repo_valid?
       puts "Updating #{@clone}"
-      Dir.chdir(@clone) { safe_system bzrpath, 'update' }
+      @clone.cd { safe_system bzrpath, 'update' }
+    elsif @clone.exist?
+      puts "Removing invalid bzr repo from cache"
+      @clone.rmtree
+      clone_repo
+    else
+      clone_repo
     end
   end
 
+  def clone_repo
+    url = @url.sub(%r[^bzr://], '')
+    # 'lightweight' means history-less
+    safe_system bzrpath, 'checkout', '--lightweight', url, @clone
+  end
+
   def stage
     # FIXME: The export command doesn't work on checkouts
     # See https://bugs.launchpad.net/bzr/+bug/897511