diff --git a/pkg/parser/schema_errors.go b/pkg/parser/schema_errors.go
index 00868f3c2ba..a190ccb2b6a 100644
--- a/pkg/parser/schema_errors.go
+++ b/pkg/parser/schema_errors.go
@@ -225,6 +225,9 @@ func rewriteAdditionalPropertiesError(message string) string {
 	return message
 }
 
+// normalizeAdditionalPropertyList strips quotes, trims whitespace, and sorts the
+// comma-separated property names so that diagnostics are deterministic regardless
+// of the order in which the schema validator emits them.
 func normalizeAdditionalPropertyList(raw string) string {
 	raw = strings.ReplaceAll(raw, "'", "")
 	parts := strings.Split(raw, ",")
diff --git a/pkg/parser/schema_errors_test.go b/pkg/parser/schema_errors_test.go
index 37608a391e4..bcb707edef3 100644
--- a/pkg/parser/schema_errors_test.go
+++ b/pkg/parser/schema_errors_test.go
@@ -301,7 +301,8 @@ func TestRewriteAdditionalPropertiesErrorOrdering(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			got := rewriteAdditionalPropertiesError(tt.in)
-			assert.Equal(t, tt.want, got)
+			assert.Equal(t, tt.want, got,
+				"rewriteAdditionalPropertiesError(%q) = %q, want %q", tt.in, got, tt.want)
 		})
 	}
 }