diff --git a/Gemfile b/Gemfile
index 681262e4..fd3ad996 100644
--- a/Gemfile
+++ b/Gemfile
@@ -143,3 +143,7 @@ gem "matrix"  # removed from stndard library in ruby 3.1
 gem "nkf"
 # /d/rlafage/workspace/WhatsOpt/test/test_helper.rb:3: warning: /dtis-app/rvm/rubies/ruby-3.3.5/lib/ruby/3.3.0/csv.rb was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.4.0.
 gem "csv"
+
+# Fix stringio version required by passenger in production
+gem "stringio", "3.1.1"
+
diff --git a/Gemfile.lock b/Gemfile.lock
index 9626bb0c..41262579 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -433,7 +433,7 @@ GEM
       net-sftp (>= 2.1.2)
       net-ssh (>= 2.8.0)
       ostruct
-    stringio (3.1.2)
+    stringio (3.1.1)
     sucker_punch (3.2.0)
       concurrent-ruby (~> 1.0)
     terser (1.2.4)
@@ -529,6 +529,7 @@ DEPENDENCIES
   spring
   sprockets-rails
   sqlite3
+  stringio (= 3.1.1)
   sucker_punch
   terser
   thrift (~> 0.20)