gistfile1.diff

diff --git a/lib/themeroller.image.js b/lib/themeroller.image.js
index 2acf1df..f7aa855 100644
--- a/lib/themeroller.image.js
+++ b/lib/themeroller.image.js
@@ -51,6 +51,7 @@ function stream2Buffer( callback ) {
 
 var generateIcon, generateImage, generateTexture,
  cacheDirectory = __dirname + "/../tmp/cache",
+	cachingLock = {},
 	concurrentQueues = 4,
 	imageQueue = async.queue( function( task, callback ) {
 		task( callback );
@@ -210,9 +211,13 @@ Image.prototype = {
 		fs.readFile( cacheFile, function( err, data ) {
 			if ( err ) {
 				generateImage( params, function( err, data ) {
-					if ( !err ) {
+					if ( !err && !cachingLock[ cacheFile ] ) {
 						// Write file asynchronously while sending data to callback.
-						fs.writeFile( cacheFile, data );
+						cachingLock[ cacheFile ] = true;
+						fs.writeFile( cacheFile + ".part", data, function() {
+							fs.rename( cacheFile + ".part", cacheFile );
+							delete cachingLock[ cacheFile ];
+						});
 					}
 					callback( err, filename, data );
 				});