diff --git a/java/invalid_implementation_jar.sh b/java/invalid_implementation_jar.sh
new file mode 100755
index 0000000..3820058
--- /dev/null
+++ b/java/invalid_implementation_jar.sh
@@ -0,0 +1,61 @@
+#!/bin/bash
+
+# Copyright 2022 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Script to detect and report an attempt to access an invalid implementation
+# jar.
+
+MOD=$1
+
+cat <<EOF
+
+    $MOD is a java_library that generates a jar file which must not be accessed
+    from outside the mainline module that provides it. If you are seeing this
+    message it means that you are incorrectly attempting to use the jar file
+    from a java_import prebuilt of $MOD.
+
+    This is most likely due to an incorrect dependency on $MOD in an Android.mk
+    or Android.bp file. Please remove that dependency and replace with
+    something more appropriate, e.g. a dependency on an API provided by the
+    module.
+
+    If you do not know where the extraneous dependency was added then you can
+    run the following command to find a list of all the paths from the target
+    which you are trying to build to the target which produced this error.
+
+        prebuilts/build-tools/linux-x86/bin/ninja -f out/combined-\${TARGET_PRODUCT}.ninja -t path <target> <invalid-jar>
+
+    Where <target> is the build target you specified on the command line which
+    produces this error and <invalid-jar> is the rule that failed with this
+    message. If you are specifying multiple build targets then you will need to
+    run the above command for every target until you find the cause.
+
+    The command will output one (of the possibly many) dependency paths from
+    <target> to <invalid-jar>, one file/phony target per line. e.g. it may
+    output something like this:
+
+        ....
+        out/soong/.intermediates/acme/broken/android_common/combined/broken.jar
+        out/soong/.intermediates/prebuilts/module_sdk/art/current/sdk/prebuilt_core-libart/android_common/combined/core-libart.jar
+        out/soong/.intermediates/prebuilts/module_sdk/art/current/sdk/art-module-sdk_core-libart-error/gen/this-file-will-never-be-created.jar
+
+    The last line is the failing target, the second to last line is a dependency
+    from the core-libart java_import onto the failing target, the third to last
+    line is the source of the dependency so you should look in acme/Android.bp
+    file for the "broken" module.
+
+EOF
+
+exit 1