diff --git a/tools/bootconfig/samples/bad-override.bconf b/tools/bootconfig/samples/bad-override.bconf
new file mode 100644
index 000000000000..fde6c561512e
--- /dev/null
+++ b/tools/bootconfig/samples/bad-override.bconf
@@ -0,0 +1,3 @@
+key.subkey = value
+# We can not override pre-defined subkeys with value
+key := value
diff --git a/tools/bootconfig/samples/bad-override2.bconf b/tools/bootconfig/samples/bad-override2.bconf
new file mode 100644
index 000000000000..688587cb023c
--- /dev/null
+++ b/tools/bootconfig/samples/bad-override2.bconf
@@ -0,0 +1,3 @@
+key = value
+# We can not override pre-defined value with subkey
+key.subkey := value
diff --git a/tools/bootconfig/samples/good-override.bconf b/tools/bootconfig/samples/good-override.bconf
new file mode 100644
index 000000000000..7d31d5f8fbd8
--- /dev/null
+++ b/tools/bootconfig/samples/good-override.bconf
@@ -0,0 +1,6 @@
+# Override the value
+key.word = 1,2,4
+key.word := 2,3
+
+# No pre-defined key
+key.new.word := "new"
diff --git a/tools/bootconfig/test-bootconfig.sh b/tools/bootconfig/test-bootconfig.sh
index 3c2ab9e75730..56284b98d8f0 100755
--- a/tools/bootconfig/test-bootconfig.sh
+++ b/tools/bootconfig/test-bootconfig.sh
@@ -117,6 +117,19 @@ xpass grep -q "bar" $OUTFILE
 xpass grep -q "baz" $OUTFILE
 xpass grep -q "qux" $OUTFILE
 
+echo "Override same-key values"
+cat > $TEMPCONF << EOF
+key = bar, baz
+key := qux
+EOF
+echo > $INITRD
+
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $OUTFILE
+xfail grep -q "bar" $OUTFILE
+xfail grep -q "baz" $OUTFILE
+xpass grep -q "qux" $OUTFILE
+
 echo "Double/single quotes test"
 echo "key = '\"string\"';" > $TEMPCONF
 $BOOTCONF -a $TEMPCONF $INITRD