diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 79b1f51cc..5db40e833 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -77,7 +77,7 @@ jobs:
           # check if there is a specific Sphinx version to test with
           # example substitution: tox run -e compile,py39-sphinx61-tests
           if [ -n "${{matrix.sphinx-version}}" ]; then
-            python -Im tox run -e compile,py$(echo ${{ matrix.python-version }} | tr -d .)-sphinx(echo ${{ matrix.sphinx-version }} | tr -d .)-tests
+            python -Im tox run -e compile,py$(echo ${{ matrix.python-version }} | tr -d .)-sphinx$(echo ${{ matrix.sphinx-version }} | tr -d .)-tests
           # if not we use the default version
           # example substitution: tox run -e compile,py39-tests
           else