diff --git a/.circleci/python_job.bash b/.circleci/python_job.bash
index d804f2b27f..15999c92d4 100644
--- a/.circleci/python_job.bash
+++ b/.circleci/python_job.bash
@@ -114,10 +114,10 @@ function run_check_glean {
     local HAS_DIFFS=0
     local HAS_FILES=0
     local EXIT_CODE=0
-    for FILENAME in `find ${GLEAN_TEST_FOLDER} -type f -exec basename \{\} \;`
+    for FILENAME in `find ${GLEAN_TEST_FOLDER} -type f -name '*.py' -exec basename \{\} \;`
     do
         HAS_FILES=1
-        if [[ 0 -ne `cmp --silent "${GLEAN_TEST_FOLDER}/${FILENAME}" "${GLEAN_OUTPUT_FOLDER}/${FILENAME}"` ]]
+        if /usr/bin/cmp --silent "${GLEAN_TEST_FOLDER}/${FILENAME}" "${GLEAN_OUTPUT_FOLDER}/${FILENAME}"
         then
             HAS_DIFFS=1
         fi
@@ -130,7 +130,8 @@ function run_check_glean {
     if [ $HAS_DIFFS -eq 1 ]
     then
         echo "*** Differences detected - need to re-run glean_parser ***"
-        diff $GLEAN_OUTPUT_FOLDER $GLEAN_TEST_FOLDER
+        diff --exclude '__pycache__' $GLEAN_OUTPUT_FOLDER $GLEAN_TEST_FOLDER || true
+        echo "*** End of differences***"
         EXIT_CODE=1
     fi
     if [ "$GLEAN_TEST_FOLDER" != "" ]
@@ -141,6 +142,15 @@ function run_check_glean {
     if [ $EXIT_CODE -eq 0 ]
     then
         echo "✓ Files are identical"
+    elif [ $HAS_DIFFS -eq 1 ]
+    then
+        echo
+        echo "To fix, run:"
+        echo
+        echo "  bash .circleci/python_job.bash run build_glean"
+        echo
+        echo "and add as a commit to this pull request."
+        exit 1
     else
         exit 1
     fi