diff --git a/src/opt/publisher/Gemfile b/src/opt/publisher/Gemfile
index f487110..814b911 100644
--- a/src/opt/publisher/Gemfile
+++ b/src/opt/publisher/Gemfile
@@ -1,3 +1,3 @@
 source "https://rubygems.org"
 
-gem 'govuk_tech_docs', '~> 3.4'
+gem 'govuk_tech_docs', '3.4.0'
diff --git a/src/opt/publisher/Gemfile.lock b/src/opt/publisher/Gemfile.lock
index 06adf47..4559299 100644
--- a/src/opt/publisher/Gemfile.lock
+++ b/src/opt/publisher/Gemfile.lock
@@ -186,7 +186,7 @@ PLATFORMS
   x86_64-linux-musl
 
 DEPENDENCIES
-  govuk_tech_docs (~> 3.4)
+  govuk_tech_docs (= 3.4.0)
 
 BUNDLED WITH
    2.5.6