diff --git a/scripts/circleci/build.sh b/scripts/circleci/build.sh
index f186f7674f483..545a2766699af 100755
--- a/scripts/circleci/build.sh
+++ b/scripts/circleci/build.sh
@@ -5,7 +5,12 @@ set -e
 # Update the local size measurements to the master version
 # so that the size diff printed at the end of the build is
 # accurate.
-curl -o scripts/rollup/results.json http://react.zpao.com/builds/master/latest/results.json
+merge_base_hash=`git merge-base HEAD master`
+timestamp=`git log --format='%ct' -1 $merge_base_hash`
+json_url=http://react.zpao.com/builds/master/$timestamp-$merge_base_hash/results.json
+echo Downloading original build sizes from: $json_url
+echo $CIRCLE_COMPARE_URL
+curl -o scripts/rollup/results.json $json_url
 
 yarn build --extract-errors
 # Note: since we run the full build including extracting error codes,