diff --git a/src/components/pipelines/deal-form.tsx b/src/components/pipelines/deal-form.tsx
index 1027a6f..8e63a80 100644
--- a/src/components/pipelines/deal-form.tsx
+++ b/src/components/pipelines/deal-form.tsx
@@ -79,7 +79,9 @@ export function DealForm({
       setTitle(deal.title);
       setValue(String(deal.value ?? ""));
       setCurrency(deal.currency || "USD");
-      setContactId(deal.contact_id);
+      // contact_id is nullable when the contact has been deleted
+      // (migration 004: ON DELETE SET NULL). "" means "no selection".
+      setContactId(deal.contact_id ?? "");
       setStageId(deal.stage_id);
       setAssignedTo(deal.assigned_to ?? "");
       setExpectedCloseDate(deal.expected_close_date ?? "");
diff --git a/src/types/index.ts b/src/types/index.ts
index aed01e8..81be69e 100644
--- a/src/types/index.ts
+++ b/src/types/index.ts
@@ -141,7 +141,11 @@ export interface Deal {
   user_id: string;
   pipeline_id: string;
   stage_id: string;
-  contact_id: string;
+  /**
+   * Nullable after migration 004 — becomes NULL when the referenced
+   * contact is deleted (ON DELETE SET NULL). History preserved.
+   */
+  contact_id: string | null;
   conversation_id?: string;
   assigned_to?: string;
   title: string;
@@ -182,7 +186,12 @@ export interface Broadcast {
 export interface BroadcastRecipient {
   id: string;
   broadcast_id: string;
-  contact_id: string;
+  /**
+   * Nullable after migration 004 — becomes NULL when the referenced
+   * contact is deleted (ON DELETE SET NULL). History preserved; the
+   * UI renders "Unknown" for orphaned rows.
+   */
+  contact_id: string | null;
   status: RecipientStatus;
   sent_at?: string;
   delivered_at?: string;
diff --git a/supabase/migrations/004_contact_delete_set_null.sql b/supabase/migrations/004_contact_delete_set_null.sql
new file mode 100644
index 0000000..f326d12
--- /dev/null
+++ b/supabase/migrations/004_contact_delete_set_null.sql
@@ -0,0 +1,65 @@
+-- ============================================================
+-- Allow contact deletion without wiping history.
+--
+-- broadcast_recipients.contact_id and deals.contact_id were declared
+-- NOT NULL REFERENCES contacts(id) with no ON DELETE action, so
+-- Postgres defaults to NO ACTION. The first time a user tried to
+-- delete a contact that had ever received a broadcast or been
+-- attached to a deal, the delete failed with:
+--
+--   ERROR 23503: update or delete on table "contacts" violates
+--   foreign key constraint ... on table <other>
+--
+-- CASCADE is the wrong fix — it would silently wipe historical
+-- broadcast recipient rows (breaking audit + retroactively moving
+-- broadcasts.sent_count / delivered_count / read_count etc. via the
+-- aggregate trigger) and deal rows.
+--
+-- SET NULL is the right fix: history rows survive with a NULL
+-- contact_id. The UI is already null-safe (contact?.name ?? 'Unknown',
+-- contact?.phone, etc.).
+--
+-- Idempotent — safe to run multiple times.
+-- ============================================================
+
+-- ── broadcast_recipients.contact_id ────────────────────────────
+ALTER TABLE broadcast_recipients
+  ALTER COLUMN contact_id DROP NOT NULL;
+
+DO $$
+BEGIN
+  IF EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'broadcast_recipients_contact_id_fkey'
+      AND conrelid = 'broadcast_recipients'::regclass
+  ) THEN
+    ALTER TABLE broadcast_recipients
+      DROP CONSTRAINT broadcast_recipients_contact_id_fkey;
+  END IF;
+END $$;
+
+ALTER TABLE broadcast_recipients
+  ADD CONSTRAINT broadcast_recipients_contact_id_fkey
+    FOREIGN KEY (contact_id) REFERENCES contacts(id)
+    ON DELETE SET NULL;
+
+-- ── deals.contact_id ───────────────────────────────────────────
+ALTER TABLE deals
+  ALTER COLUMN contact_id DROP NOT NULL;
+
+DO $$
+BEGIN
+  IF EXISTS (
+    SELECT 1 FROM pg_constraint
+    WHERE conname = 'deals_contact_id_fkey'
+      AND conrelid = 'deals'::regclass
+  ) THEN
+    ALTER TABLE deals
+      DROP CONSTRAINT deals_contact_id_fkey;
+  END IF;
+END $$;
+
+ALTER TABLE deals
+  ADD CONSTRAINT deals_contact_id_fkey
+    FOREIGN KEY (contact_id) REFERENCES contacts(id)
+    ON DELETE SET NULL;