diff --git a/Dockerfile b/Dockerfile
index 3c224a786..ed0684aec 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -19,7 +19,7 @@ RUN apt-get update && apt-get install -y \
 COPY synapse /synapse/synapse/
 COPY README.rst pyproject.toml requirements.txt /synapse/
 
-RUN pip install --prefix="/install" --no-warn-script-location \
+RUN pip install --prefix="/install" --no-warn-script-location --ignore-installed \
         --no-deps -r /synapse/requirements.txt \
  && pip install --prefix="/install" --no-warn-script-location \
         --no-deps \