diff --git a/tools/check_code_size.sh b/tools/check_code_size.sh
new file mode 100755
index 0000000000..c5f0c6ffdd
--- /dev/null
+++ b/tools/check_code_size.sh
@@ -0,0 +1,23 @@
+#!/bin/bash
+#
+# This script check that changes don't lead to code size regressions.
+# (Size of the language core (== minimal port should not grow)).
+#
+
+REFERENCE=$HOME/persist/firmware.bin
+#REFERENCE=/tmp/micropython
+#TRAVIS_PULL_REQUEST=false
+
+if [ -f $REFERENCE ]; then
+    size_old=$(stat -c%s $REFERENCE)
+    size_new=$(stat -c%s minimal/build/firmware.bin)
+    echo "Old size: $size_old new size: $size_new"
+    if [ $size_new -gt $size_old ]; then
+        echo "Validation failure: Core code size increased"
+        if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then
+            exit 1
+        fi
+    fi
+else
+    echo "Warning: reference file doesn't exist, code size check didn't run"
+fi