diff --git a/Lib/dis.py b/Lib/dis.py
index 10e5f7f..e289e17 100644
--- a/Lib/dis.py
+++ b/Lib/dis.py
@@ -542,7 +542,7 @@
     import argparse
 
     parser = argparse.ArgumentParser()
-    parser.add_argument('infile', type=argparse.FileType(), nargs='?', default='-')
+    parser.add_argument('infile', type=argparse.FileType('rb'), nargs='?', default='-')
     args = parser.parse_args()
     with args.infile as infile:
         source = infile.read()