diff --git a/lib/simplecov/result_merger.rb b/lib/simplecov/result_merger.rb
index c114463e..c9c05971 100644
--- a/lib/simplecov/result_merger.rb
+++ b/lib/simplecov/result_merger.rb
@@ -13,7 +13,11 @@ def resultset_path
     # Loads the cached resultset from YAML and returns it as a Hash
     def resultset
       if stored_data
-        SimpleCov::JSON.parse(stored_data)
+        begin
+          SimpleCov::JSON.parse(stored_data)
+        rescue
+          {}
+        end
       else
         {}
       end
@@ -66,6 +70,7 @@ def store_result(result)
       command_name, data = result.to_hash.first
       new_set[command_name] = data
       File.open(resultset_path, "w+") do |f|
+        f.flock(File::LOCK_EX)
         f.puts SimpleCov::JSON.dump(new_set)
       end
       true