diff --git a/mp3_tagger/mp3.py b/mp3_tagger/mp3.py
index 519cbfd..08f7815 100644
--- a/mp3_tagger/mp3.py
+++ b/mp3_tagger/mp3.py
@@ -84,7 +84,7 @@ def open(self):
         :return: byte string.
 
         """
-        if self.path.endswith('.mp3'):
+        if self.path.lower().endswith('.mp3'):
             try:
                 stream = open(self.path, 'r+b')
             except PermissionError: