diff --git a/tests/combine_maps.py b/tests/combine_maps.py
new file mode 100644
index 0000000..a2bf38d
--- /dev/null
+++ b/tests/combine_maps.py
@@ -0,0 +1,66 @@
+# Copyright 2018 - The Android Open Source Project
+#
+# 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.
+
+"""Tool to combine SEPolicy mapping file.
+
+Say, x, y, z are platform SEPolicy versions such that x > y > z. Then given two
+mapping files from x to y (top) and y to z (bottom), it's possible to construct
+a mapping file from x to z. We do the following to combine two maps.
+1. Add all new types declarations from top to bottom.
+2. Say, a new type "bar" in top is mapped like this "foo_V_v<-bar", then we map
+"bar" to whatever "foo" is mapped to in the bottom map. We do this for all new
+types in the top map.
+
+More generally, we can correctly construct x->z from x->y' and y"->z as long as
+y">y'.
+
+This file contains the implementation of combining two mapping files.
+"""
+import argparse
+import re
+from mini_parser import MiniCilParser
+
+def Combine(top, bottom):
+    bottom.types.update(top.types)
+
+    for top_ta in top.typeattributesets:
+        top_type_set = top.typeattributesets[top_ta]
+        if len(top_type_set) == 1:
+            continue
+
+        m = re.match(r"(\w+)_\d+_\d+", top_ta)
+        # Typeattributes in V.v.cil have _V_v suffix, but not in V.v.ignore.cil
+        bottom_type = m.group(1) if m else top_ta
+
+        for bottom_ta in bottom.rTypeattributesets[bottom_type]:
+            bottom.typeattributesets[bottom_ta].update(top_type_set)
+
+    return bottom
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("-t", "--top-map", dest="top_map",
+                        required=True, help="top map file")
+    parser.add_argument("-b", "--bottom-map", dest="bottom_map",
+                        required=True, help="bottom map file")
+    parser.add_argument("-o", "--output-file", dest="output_file",
+                        required=True, help="output map file")
+    args = parser.parse_args()
+
+    top_map_cil = MiniCilParser(args.top_map)
+    bottom_map_cil = MiniCilParser(args.bottom_map)
+    result = Combine(top_map_cil, bottom_map_cil)
+
+    with open(args.output_file, "w") as output:
+        output.write(result.unparse())