--- a/build/mozconfig.cache
+++ b/build/mozconfig.cache
@@ -1,14 +1,17 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 # Setup for build cache
 
+# Avoid duplication if the file happens to be included twice.
+if test -z "$bucket"; then
+
 read branch platform master <<EOF
 $(python2.7 -c 'import json; p = json.loads(open("'"$topsrcdir"'/../buildprops.json").read())["properties"]; print p["branch"], p["platform"], p["master"]' 2> /dev/null)
 EOF
 
 bucket=
 if test -z "$SCCACHE_DISABLE" -a -z "$no_sccache"; then
     case "${branch}_${master}" in
     try_*scl1.mozilla.com*|try_*.scl3.mozilla.com*)
@@ -57,8 +60,10 @@ else
         # For now, sccache doesn't support separate PDBs so force debug info to be
         # in object files.
         mk_add_options "export COMPILE_PDB_FLAG="
         mk_add_options "export HOST_PDB_FLAG="
         mk_add_options "export MOZ_DEBUG_FLAGS=-Z7"
         ;;
     esac
 fi
+
+fi