diff --git a/project/build.xml b/project/build.xml
index 4073e11ef..a10a91491 100644
--- a/project/build.xml
+++ b/project/build.xml
@@ -4,7 +4,7 @@
     <!-- The local.properties file is created and updated by the 'android' tool.
          It contains the path to the SDK. It should *NOT* be checked into
          Version Control Systems. -->
-    <loadproperties srcFile="local.properties" />
+    <property file="local.properties" />
 
     <!-- The ant.properties file can be created by you. It is only edited by the
          'android' tool to add properties to it.
@@ -28,6 +28,15 @@
          -->
     <property file="ant.properties" />
 
+    <!-- if sdk.dir was not set from one of the property file, then
+         get it from the ANDROID_HOME env var.
+         This must be done before we load project.properties since
+         the proguard config can use sdk.dir -->
+    <property environment="env" />
+    <condition property="sdk.dir" value="${env.ANDROID_HOME}">
+        <isset property="env.ANDROID_HOME" />
+    </condition>
+
     <!-- The project.properties file is created and updated by the 'android'
          tool, as well as ADT.
 
@@ -41,25 +50,23 @@
 
     <!-- quick check on sdk.dir -->
     <fail
-            message="sdk.dir is missing. Make sure to generate local.properties using 'android update project'"
+            message="sdk.dir is missing. Make sure to generate local.properties using 'android update project' or to inject it through the ANDROID_HOME environment variable."
             unless="sdk.dir"
     />
 
-
-<!-- extension targets. Uncomment the ones where you want to do custom work
-     in between standard targets -->
-<!--
-    <target name="-pre-build">
-    </target>
-    <target name="-pre-compile">
-    </target>
-
-    /* This is typically used for code obfuscation.
-       Compiled code location: ${out.classes.absolute.dir}
-       If this is not done in place, override ${out.dex.input.absolute.dir} */
-    <target name="-post-compile">
-    </target>
--->
+    <!--
+        Import per project custom build rules if present at the root of the project.
+        This is the place to put custom intermediary targets such as:
+            -pre-build
+            -pre-compile
+            -post-compile (This is typically used for code obfuscation.
+                           Compiled code location: ${out.classes.absolute.dir}
+                           If this is not done in place, override ${out.dex.input.absolute.dir})
+            -post-package
+            -post-build
+            -pre-clean
+    -->
+    <import file="custom_rules.xml" optional="true" />
 
     <!-- Import the actual build file.