diff --git a/test/lint/git-subtree-check.sh b/test/lint/git-subtree-check.sh
--- a/test/lint/git-subtree-check.sh
+++ b/test/lint/git-subtree-check.sh
@@ -41,21 +41,17 @@
 	done
 }
 
+# find latest subtree update
 latest_squash="$(find_latest_squash "$DIR")"
 if [ -z "$latest_squash" ]; then
     echo "ERROR: $DIR is not a subtree" >&2
     exit 2
 fi
-
 set $latest_squash
 old=$1
 rev=$2
-if [ "d$(git cat-file -t $rev 2>/dev/null)" != dcommit ]; then
-    echo "ERROR: subtree commit $rev unavailable. Fetch/update the subtree repository" >&2
-    exit 2
-fi
-tree_subtree=$(git show -s --format="%T" $rev)
-echo "$DIR in $COMMIT was last updated to upstream commit $rev (tree $tree_subtree)"
+
+# get the tree in the current commit
 tree_actual=$(git ls-tree -d "$COMMIT" "$DIR" | head -n 1)
 if [ -z "$tree_actual" ]; then
     echo "FAIL: subtree directory $DIR not found in $COMMIT" >&2
@@ -69,9 +65,30 @@
     echo "FAIL: subtree directory $DIR is not a tree in $COMMIT" >&2
     exit 1
 fi
+
+# get the tree at the time of the last subtree update
+tree_commit=$(git show -s --format="%T" $old)
+echo "$DIR in $COMMIT was last updated in commit $old (tree $tree_commit)"
+
+# ... and compare the actual tree with it
+if [ "$tree_actual_tree" != "$tree_commit" ]; then
+    git diff $tree_commit $tree_actual_tree >&2
+    echo "FAIL: subtree directory was touched without subtree merge" >&2
+    exit 1
+fi
+
+# get the tree in the subtree commit referred to
+if [ "d$(git cat-file -t $rev 2>/dev/null)" != dcommit ]; then
+    echo "subtree commit $rev unavailable: cannot compare" >&2
+    exit
+fi
+tree_subtree=$(git show -s --format="%T" $rev)
+echo "$DIR in $COMMIT was last updated to upstream commit $rev (tree $tree_subtree)"
+
+# ... and compare the actual tree with it
 if [ "$tree_actual_tree" != "$tree_subtree" ]; then
-    git diff-tree $tree_actual_tree $tree_subtree >&2
-    echo "FAIL: subtree directory tree doesn't match subtree commit tree" >&2
+    echo "FAIL: subtree update commit differs from upstream tree!" >&2
     exit 1
 fi
+
 echo "GOOD"