diff --git a/hammer b/hammer
index a95774dd39..129c68d57e 100755
--- a/hammer
+++ b/hammer
@@ -1,8 +1,27 @@
 #!/bin/sh
+#
+# Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# A script to invoke scons in gyp generated projects.
+
+# Find the 'src' directory by looking for the site_scons directory.
+# This method allows trees that don't use the name src to use this script.
+# Explicitly skip site_scons directories that are from the 'software
+# construction toolkit', since these are not gyp compatible.
+SRC_DIR=`pwd`
+while `test ! -d "${SRC_DIR}/site_scons" -o \
+       -e "${SRC_DIR}/site_scons/site_tools/component_setup.py"`; do
+  PARENT_DIR="$(dirname ${SRC_DIR})"
+  if `test "${SRC_DIR}" == "${PARENT_DIR}"`; then
+    echo "ERROR: hammer must be run in a directory with site_scons under" >&2
+    echo "       the root of the project tree." >&2
+    exit 1
+  fi
+  SRC_DIR="${PARENT_DIR}"
+done
 
-# The first expression catches when we're actually in the /src directory.
-# The second expressions strips everything after the last /src occurrence.
-SRC_DIR=`pwd | sed -e '\;/src$;q' -e 's;\(.*/src\)/.*;\1;'`
 SCONS="${SRC_DIR}/third_party/scons/scons.py"
 SITE_SCONS="${SRC_DIR}/site_scons"