diff --git a/core/Makefile b/core/Makefile
index 0af846e..5d4a283 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -51,6 +51,7 @@
 	        echo "#" >> $@;
 	$(hide) $(foreach line,$(ADDITIONAL_DEFAULT_PROPERTIES), \
 		echo "$(line)" >> $@;)
+	build/tools/post_process_props.py $@
 
 # -----------------------------------------------------------------
 # build.prop
@@ -161,6 +162,7 @@
 		        echo "#" >> $@; )
 	$(hide) $(foreach line,$(ADDITIONAL_BUILD_PROPERTIES), \
 		echo "$(line)" >> $@;)
+	$(hide) build/tools/post_process_props.py $@
 
 build_desc :=
 
diff --git a/tools/post_process_props.py b/tools/post_process_props.py
new file mode 100755
index 0000000..83e1431
--- /dev/null
+++ b/tools/post_process_props.py
@@ -0,0 +1,83 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2009 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.
+
+import sys
+
+# Put the modifications that you need to make into the /system/build.prop into this
+# function. The prop object has get(name) and put(name,value) methods.
+def mangle_build_prop(prop):
+  pass
+
+
+# Put the modifications that you need to make into the /system/build.prop into this
+# function. The prop object has get(name) and put(name,value) methods.
+def mangle_default_prop(prop):
+  # If ro.debuggable is 1, then enable adb on USB by default
+  # (this is for userdebug builds)
+  if prop.get("ro.debuggable") == "1":
+    val = prop.get("persist.sys.usb.config")
+    if val == "":
+      val = "adb"
+    else:
+      val = val + ",adb"
+    prop.put("persist.sys.usb.config", val)
+
+
+class PropFile:
+  def __init__(self, lines):
+    self.lines = [s[:-1] for s in lines]
+
+  def get(self, name):
+    key = name + "="
+    for line in self.lines:
+      if line.startswith(key):
+        return line[len(key):]
+    return ""
+
+  def put(self, name, value):
+    key = name + "="
+    for i in range(0,len(self.lines)):
+      if self.lines[i].startswith(key):
+        self.lines[i] = key + value
+        return
+    self.lines.append(key + value)
+
+  def write(self, f):
+    f.write("\n".join(self.lines))
+    f.write("\n")
+
+def main(argv):
+  filename = argv[1]
+  f = open(filename)
+  lines = f.readlines()
+  f.close()
+
+  properties = PropFile(lines)
+  if filename.endswith("/build.prop"):
+    mangle_build_prop(properties)
+  elif filename.endswith("/default.prop"):
+    mangle_default_prop(properties)
+  else:
+    sys.stderr.write("bad command line: " + str(argv) + "\n")
+    sys.exit(1)
+
+  f = open(filename)
+  #properties.write(f)
+  properties.write(sys.stdout)
+  f.close()
+
+if __name__ == "__main__":
+  main(sys.argv)