diff --git a/ci/drone.yml b/ci/drone.yml
index 0eb4b7a..82dbc36 100644
--- a/ci/drone.yml
+++ b/ci/drone.yml
@@ -14,6 +14,7 @@ steps:
 - name: Linux test
   image: ad5001/ubuntu-pyside2-xvfb:hirsute-5.15.2
   commands:
+  - pip3 install sympy
   - xvfb-run python3 run.py --test-build --no-check-for-updates
   - xvfb-run python3 run.py --test-build --no-check-for-updates ./ci/test1.lpf
   - xvfb-run python3 run.py --test-build --no-check-for-updates ./ci/test2.lpf
@@ -24,6 +25,7 @@ steps:
   image: ad5001/ubuntu-pyside2-xvfb-wine:win7-5.15.2
   commands:
   - # For some reason, launching GUI apps with wine, even with xvfb-run, fails.
+  - pip install sympy
   - xvfb-run python run.py --test-build --no-check-for-updates
   - xvfb-run python run.py --test-build --no-check-for-updates ./ci/test1.lpf
   - xvfb-run python run.py --test-build --no-check-for-updates ./ci/test2.lpf