diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 5b47f1fa228b27e17efd5090865ff28d0e034b1b..559950000a882c28d4985fd356ada8e61074f2cf 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -96,7 +96,7 @@ tests:
     - chmod +x ./CI/update_badge.sh
     - ./CI/update_badge.sh > /dev/null
   script:
-    - pip uninstall six
+    - pip install six==1.15.0
     - pip install -r requirements.txt
     - chmod +x ./CI/run_pytest.sh
     - ./CI/run_pytest.sh
@@ -121,7 +121,7 @@ coverage:
     - chmod +x ./CI/update_badge.sh
     - ./CI/update_badge.sh > /dev/null
   script:
-    - pip uninstall six
+    - pip install six==1.15.0
     - pip install -r requirements.txt
     - chmod +x ./CI/run_pytest_coverage.sh
     - ./CI/run_pytest_coverage.sh
@@ -144,7 +144,7 @@ sphinx docs:
     - chmod +x ./CI/update_badge.sh
     - ./CI/update_badge.sh > /dev/null
   script:
-    - pip uninstall six
+    - pip install six==1.15.0
     - pip install -r requirements.txt
     - pip install -r docs/requirements_docs.txt
     - chmod +x ./CI/create_documentation.sh