diff --git a/ee/app/models/ee/ci/build.rb b/ee/app/models/ee/ci/build.rb
index ed7e9c397e776b94b7714c295b53891a0e8af19a..88732f749467e1664e381e3dbb460ab044ccde20 100644
--- a/ee/app/models/ee/ci/build.rb
+++ b/ee/app/models/ee/ci/build.rb
@@ -223,7 +223,7 @@ def pages
 
         (options&.dig(:pages) || {}).tap do |pages_options|
           if ::Gitlab::Pages.multiple_versions_enabled_for?(project)
-            pages_options[:path_prefix] = ExpandVariables.expand(pages_options[:path_prefix], -> {
+            pages_options[:path_prefix] = ExpandVariables.expand(pages_options[:path_prefix].to_s, -> {
               variables.sort_and_expand_all
             })
           else
diff --git a/ee/spec/models/ci/build_spec.rb b/ee/spec/models/ci/build_spec.rb
index 9f5ee4916fea5bd09cd652522ca7a88fb4e7fc0a..5fce23af024ff39e0efd753c84febce628acb5de 100644
--- a/ee/spec/models/ci/build_spec.rb
+++ b/ee/spec/models/ci/build_spec.rb
@@ -985,6 +985,7 @@
       false | false | { pages: { path_prefix: 'foo' } } | {}
       false | true | { pages: { path_prefix: 'foo' } } | {}
       true | false | { pages: { path_prefix: 'foo' } } | {}
+      true | true | { pages: { path_prefix: nil } } | { path_prefix: '' }
       true | true | { pages: { path_prefix: 'foo' } } | { path_prefix: 'foo' }
       true | true | { pages: { path_prefix: '$CI_COMMIT_BRANCH' } } | { path_prefix: 'master' }
     end