diff --git a/.gitignore b/.gitignore
index 9b69c0a..b69a35d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@ dpaste/static/
 dpaste.egg-info
 dpaste.sqlite
 node_modules
+**/__pycache__/
\ No newline at end of file
diff --git a/dpaste/views.py b/dpaste/views.py
index 2e5fdff..123c12d 100644
--- a/dpaste/views.py
+++ b/dpaste/views.py
@@ -13,6 +13,7 @@ from django.http import (
 from django.shortcuts import get_object_or_404, render
 from django.urls import reverse
 from django.utils import timezone
+from django.utils.html import escape
 from django.utils.cache import add_never_cache_headers, patch_cache_control
 from django.utils.translation import gettext
 from django.views.generic import FormView
@@ -290,8 +291,7 @@ class APIView(View):
         # A lexer is given, check if its valid at all
         if lexer and lexer not in highlight.LEXER_KEYS:
             return HttpResponseBadRequest(
-                'Invalid lexer "%s" given. Valid lexers are: %s'
-                % (lexer, ", ".join(highlight.LEXER_KEYS))
+                f'Invalid lexer choice "{escape(lexer)}" given. Valid lexer values are: {", ".join(highlight.LEXER_KEYS)}'
             )
 
         # No lexer is given, but we have a filename, try to get the lexer
@@ -308,9 +308,7 @@ class APIView(View):
             expire_options = [str(i) for i in dict(config.EXPIRE_CHOICES)]
             if expires not in expire_options:
                 return HttpResponseBadRequest(
-                    'Invalid expire choice "{}" given. Valid values are: {}'.format(
-                        expires, ", ".join(expire_options)
-                    )
+                    f'Invalid expire choice "{escape(expires)}" given. Valid expire values are: {", ".join(expire_options)}'
                 )
             expires, expire_type = get_expire_values(expires)
         else:
@@ -352,4 +350,4 @@ def handler500(request, template_name="dpaste/500.html"):
     context.update(config.extra_template_context)
     response = render(request, template_name, context, status=500)
     add_never_cache_headers(response)
-    return response
+    return response
\ No newline at end of file