diff --git a/Classes/FlickrKit/FlickrKit.m b/Classes/FlickrKit/FlickrKit.m
index dc574d5..66ee77d 100644
--- a/Classes/FlickrKit/FlickrKit.m
+++ b/Classes/FlickrKit/FlickrKit.m
@@ -438,7 +438,8 @@ - (NSURL *) photoURLForSize:(FKPhotoSize)size photoID:(NSString *)photoID server
 	[URLString appendFormat:@"%@/%@_%@", server, photoID, secret];
 	
 	NSString *sizeKey = FKIdentifierForSize(size);
-	[URLString appendFormat:@"_%@.jpg", sizeKey];
+    if(sizeKey.length > 0)
+        [URLString appendFormat:@"_%@.jpg", sizeKey];
     
 	return [NSURL URLWithString:URLString];
 }