diff --git a/SDWebImage/SDImageCache.m b/SDWebImage/SDImageCache.m
index 36bb751..3797967 100644
--- a/SDWebImage/SDImageCache.m
+++ b/SDWebImage/SDImageCache.m
@@ -134,8 +134,9 @@ BOOL ImageDataHasPNGPreffix(NSData *data) {
     }
     unsigned char r[CC_MD5_DIGEST_LENGTH];
     CC_MD5(str, (CC_LONG)strlen(str), r);
-    NSString *filename = [NSString stringWithFormat:@"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",
-                                                    r[0], r[1], r[2], r[3], r[4], r[5], r[6], r[7], r[8], r[9], r[10], r[11], r[12], r[13], r[14], r[15]];
+    NSString *filename = [NSString stringWithFormat:@"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x.%@",
+                                                    r[0], r[1], r[2], r[3], r[4], r[5], r[6], r[7], r[8], r[9], r[10], r[11], r[12], r[13], r[14], r[15],
+                                                    [key pathExtension]];
 
     return filename;
 }