diff --git a/.github/workflows/4_2_11.yml b/.github/workflows/4_2_11.yml
index b3d886f..2bd0d4c 100644
--- a/.github/workflows/4_2_11.yml
+++ b/.github/workflows/4_2_11.yml
@@ -89,6 +89,8 @@ jobs:
       - name: Prepare Redmine source
         working-directory: redmine
         run: |
+          # TODO Remove the following line when https://www.redmine.org/issues/40551 is fixed
+          sed -i -e 's/.*mocha.*/  gem "mocha", "2.1.0"/' Gemfile # Fix core tests not compatible with Mocha 2.2.0 
           sed -i '/rubocop/d' Gemfile
           rm -f .rubocop*
           cp plugins/redmine_base_rspec/spec/support/database-${{ matrix.db }}.yml config/database.yml
diff --git a/.github/workflows/5_1_2.yml b/.github/workflows/5_1_2.yml
index 5a6c8c0..c9cb14e 100644
--- a/.github/workflows/5_1_2.yml
+++ b/.github/workflows/5_1_2.yml
@@ -89,6 +89,8 @@ jobs:
       - name: Prepare Redmine source
         working-directory: redmine
         run: |
+          # TODO Remove the following line when https://www.redmine.org/issues/40551 is fixed
+          sed -i -e 's/.*mocha.*/  gem "mocha", "2.1.0"/' Gemfile # Fix core tests not compatible with Mocha 2.2.0 
           rm -f test/integration/routing/plugins_test.rb # Fix routing tests # TODO Remove this line when https://www.redmine.org/issues/38707 is fixed
           sed -i '/rubocop/d' Gemfile
           rm -f .rubocop*
diff --git a/.github/workflows/master.yml b/.github/workflows/master.yml
index 33907be..470834d 100644
--- a/.github/workflows/master.yml
+++ b/.github/workflows/master.yml
@@ -89,6 +89,8 @@ jobs:
       - name: Prepare Redmine source
         working-directory: redmine
         run: |
+          # TODO Remove the following line when https://www.redmine.org/issues/40551 is fixed
+          sed -i -e 's/.*mocha.*/  gem "mocha", "2.1.0"/' Gemfile # Fix core tests not compatible with Mocha 2.2.0 
           sed -i '/rubocop/d' Gemfile
           rm -f .rubocop*
           cp plugins/redmine_base_rspec/spec/support/database-${{ matrix.db }}.yml config/database.yml