diff --git a/3.7/Dockerfile b/3.7/Dockerfile
index a636e79..792fa94 100644
--- a/3.7/Dockerfile
+++ b/3.7/Dockerfile
@@ -1,4 +1,4 @@
-FROM python:3.7.9-slim-buster
+FROM python:3.7.9-slim-buster@sha256:64a8d50a55ff2bc22d1f476f134549fb3775cee73d0457930e7f3d3ec8a4aa3f
 
 # renovate: datasource=pypi depName=poetry versioning=semver
 ENV POETRY_VERSION v1.1.4
diff --git a/3.8/Dockerfile b/3.8/Dockerfile
index 5509f50..2a3df9e 100644
--- a/3.8/Dockerfile
+++ b/3.8/Dockerfile
@@ -1,4 +1,4 @@
-FROM python:3.8.7-slim-buster
+FROM python:3.8.7-slim-buster@sha256:c98dca2d70689194bdd7d293af74a2c5690175ec6d1a2bcafe67068e35d5973b
 
 # renovate: datasource=pypi depName=poetry versioning=semver
 ENV POETRY_VERSION v1.1.4
diff --git a/3.9/Dockerfile b/3.9/Dockerfile
index 8fda59f..0e37bc8 100644
--- a/3.9/Dockerfile
+++ b/3.9/Dockerfile
@@ -1,4 +1,4 @@
-FROM python:3.9.1-slim-buster
+FROM python:3.9.1-slim-buster@sha256:b2013807b8af03d66f60a979f20d4e93e4e4a111df1287d9632c8cfd41ecfa33
 
 # renovate: datasource=pypi depName=poetry versioning=semver
 ENV POETRY_VERSION v1.1.4