diff --git a/doc_requirements.txt b/doc_requirements.txt
index 4afbea6cb7ab..e623125382d4 100644
--- a/doc_requirements.txt
+++ b/doc_requirements.txt
@@ -1,6 +1,6 @@
 # Note: this should disappear at some point. For now, please keep it
 #       in sync with the doc dependencies in pyproject.toml
-Sphinx!=3.1.0
+Sphinx!=3.1.0, <4.1.0
 pydata-sphinx-theme>=0.6.1
 sphinx-panels>=0.5.2
 matplotlib>2
diff --git a/pyproject.toml b/pyproject.toml
index f75c375c8963..a0c183bb6db2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -93,7 +93,7 @@ test = [
     "scikit-umfpack",
 ]
 doc = [
-    "sphinx!=3.1.0",
+    "sphinx!=3.1.0, <4.1.0",
     "pydata-sphinx-theme>=0.6.1",
     "sphinx-panels>=0.5.2",
     "matplotlib>2",