diff --git a/infra/base-images/base-image/Dockerfile b/infra/base-images/base-image/Dockerfile
index 3e0ad0fd02c6..c14adff5e411 100644
--- a/infra/base-images/base-image/Dockerfile
+++ b/infra/base-images/base-image/Dockerfile
@@ -16,7 +16,7 @@
 
 # Base image for all other images.
 
-ARG parent_image=ubuntu:20.04
+ARG parent_image=ubuntu:20.04@sha256:4a45212e9518f35983a976eead0de5eecc555a2f047134e9dd2cfc589076a00d
 
 FROM $parent_image
 
diff --git a/infra/build/functions/build_and_push_test_images.py b/infra/build/functions/build_and_push_test_images.py
index fee95e9d7970..64da29f1d811 100755
--- a/infra/build/functions/build_and_push_test_images.py
+++ b/infra/build/functions/build_and_push_test_images.py
@@ -99,7 +99,7 @@ def gcb_build_and_push_images(test_image_suffix):
     directory = os.path.join('infra', 'base-images', base_image)
     step = build_lib.get_docker_build_step([main_tag, test_tag],
                                            directory,
-                                           buildkit_cache_image=test_tag,
+                                           use_buildkit_cache=True,
                                            src_root='.')
     steps.append(step)
 
diff --git a/infra/build/functions/build_lib.py b/infra/build/functions/build_lib.py
index c22d8dc3158c..bfdb3f833d8c 100644
--- a/infra/build/functions/build_lib.py
+++ b/infra/build/functions/build_lib.py
@@ -371,7 +371,7 @@ def _make_image_name_architecture_specific(image_name, architecture):
 
 def get_docker_build_step(image_names,
                           directory,
-                          buildkit_cache_image=None,
+                          use_buildkit_cache=False,
                           src_root='oss-fuzz',
                           architecture='x86_64'):
   """Returns the docker build step."""
@@ -398,17 +398,15 @@ def get_docker_build_step(image_names,
       'args': args,
       'dir': directory,
   }
+  # Handle buildkit args
   # Note that we mutate "args" after making it a value in step.
-
-  if buildkit_cache_image is not None:
+  if use_buildkit_cache:
     env = ['DOCKER_BUILDKIT=1']
     step['env'] = env
-    assert buildkit_cache_image in args
-    additional_args = [
-        '--build-arg', 'BUILDKIT_INLINE_CACHE=1', '--cache-from',
-        buildkit_cache_image
-    ]
-    args.extend(additional_args)
+    args.extend(['--build-arg', 'BUILDKIT_INLINE_CACHE=1'])
+    for image in image_names:
+      args.extend(['--cache-from', image])
+
   args.append('.')
 
   return step