diff --git a/requirements_docs.txt b/requirements_docs.txt
index a4c1bde..d91b369 100644
--- a/requirements_docs.txt
+++ b/requirements_docs.txt
@@ -12,5 +12,5 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-sphinx>=2.0.0<9
+sphinx>=2.0.0,<9
 sphinx-bluebrain-theme