diff --git a/migrations/0171.sql b/migrations/0171.sql
new file mode 100644
index 00000000..5f2cb918
--- /dev/null
+++ b/migrations/0171.sql
@@ -0,0 +1,10 @@
+CREATE TRIGGER remove_conversions AFTER DELETE ON quantity_units
+BEGIN
+	DELETE FROM quantity_unit_conversions
+	WHERE from_qu_id = OLD.id
+		OR to_qu_id = OLD.id;
+END;
+
+DELETE FROM quantity_unit_conversions
+WHERE NOT EXISTS(SELECT 1 FROM quantity_units WHERE id = quantity_unit_conversions.from_qu_id)
+	OR NOT EXISTS(SELECT 1 FROM quantity_units WHERE id = quantity_unit_conversions.to_qu_id);