diff --git a/.ci/install.sh b/.ci/install.sh
index 30b64349d70..1810cae385f 100755
--- a/.ci/install.sh
+++ b/.ci/install.sh
@@ -35,6 +35,7 @@ python3 -m pip install defusedxml
 python3 -m pip install olefile
 python3 -m pip install -U pytest
 python3 -m pip install -U pytest-cov
+python3 -m pip install -U pytest-subinterpreter
 python3 -m pip install -U pytest-timeout
 python3 -m pip install pyroma