diff --git a/pre_commit_hooks/check_json.py b/pre_commit_hooks/check_json.py
index e1578ff..b403f4b 100644
--- a/pre_commit_hooks/check_json.py
+++ b/pre_commit_hooks/check_json.py
@@ -1,10 +1,10 @@
 from __future__ import print_function
 
 import argparse
+import io
+import json
 import sys
 
-import simplejson
-
 
 def check_json(argv=None):
     parser = argparse.ArgumentParser()
@@ -14,8 +14,8 @@
     retval = 0
     for filename in args.filenames:
         try:
-            simplejson.load(open(filename))
-        except (simplejson.JSONDecodeError, UnicodeDecodeError) as exc:
+            json.load(io.open(filename, encoding='UTF-8'))
+        except (ValueError, UnicodeDecodeError) as exc:
             print('{}: Failed to json decode ({})'.format(filename, exc))
             retval = 1
     return retval
diff --git a/pre_commit_hooks/pretty_format_json.py b/pre_commit_hooks/pretty_format_json.py
index 76b8cfb..5e04230 100644
--- a/pre_commit_hooks/pretty_format_json.py
+++ b/pre_commit_hooks/pretty_format_json.py
@@ -27,9 +27,9 @@
     )) + "\n"  # dumps does not end with a newline
 
 
-def _autofix(filename, new_contents, encoding=None):
+def _autofix(filename, new_contents):
     print("Fixing file {}".format(filename))
-    with io.open(filename, 'w', encoding=encoding) as f:
+    with io.open(filename, 'w', encoding='UTF-8') as f:
         f.write(new_contents)
 
 
@@ -100,7 +100,7 @@
     status = 0
 
     for json_file in args.filenames:
-        with io.open(json_file, encoding='utf-8') as f:
+        with io.open(json_file, encoding='UTF-8') as f:
             contents = f.read()
 
         try:
@@ -113,10 +113,7 @@
                 print("File {} is not pretty-formatted".format(json_file))
 
                 if args.autofix:
-                    _autofix(
-                        json_file, pretty_contents,
-                        encoding='utf-8' if args.no_ensure_ascii else None,
-                    )
+                    _autofix(json_file, pretty_contents)
 
                 status = 1