diff --git a/internal/config/store_postgres.go b/internal/config/store_postgres.go
index 668d1bd2..4a3e57a5 100644
--- a/internal/config/store_postgres.go
+++ b/internal/config/store_postgres.go
@@ -2408,13 +2408,24 @@ func (s *PostgresStore) StampOfferingClass(ctx context.Context, purchaseID, offe
 // token, and returns the row's values as of the claim (issue #525): the handler
 // must not trust a row read before the claim. It returns (nil, nil) when the row
 // could not be claimed (active, pending without a token, or absent).
+//
+// Rows saved before migration 000108 can share a purchase_id (#267). The claim
+// then works on the earliest row (created_at, then id), the one
+// GetPurchaseHistoryByPurchaseID returns, and refuses while any duplicate
+// records an active listing, so the returned prior state and listing id belong
+// to one row and a duplicate never reopens a listed RI.
 func (s *PostgresStore) ClaimMarketplaceListingSlot(ctx context.Context, purchaseID, clientToken string, priceSchedule []byte) (*MarketplaceListingClaim, error) {
-	// prev locks the row first, so a claim that races another one waits for it
-	// and then sees its committed token and state instead of a stale snapshot.
+	// prev locks the earliest row first, so a claim that races another one
+	// waits for it and then sees its committed token and state instead of a
+	// stale snapshot. created_at and id never change, so the row prev picks
+	// stays the earliest while it waits.
 	query := `
 		WITH prev AS (
-			SELECT purchase_id, listing_state AS prior_state
-			FROM purchase_history WHERE purchase_id = $2 FOR UPDATE
+			SELECT id, listing_state AS prior_state
+			FROM purchase_history WHERE purchase_id = $2
+			ORDER BY created_at, id
+			LIMIT 1
+			FOR UPDATE
 		)
 		UPDATE purchase_history AS p
 		SET listing_state = $1,
@@ -2422,9 +2433,14 @@ func (s *PostgresStore) ClaimMarketplaceListingSlot(ctx context.Context, purchas
 		    listing_price_schedule = CASE WHEN p.listing_client_token IS NULL
 		                                  THEN $4::jsonb ELSE p.listing_price_schedule END
 		FROM prev
-		WHERE p.purchase_id = prev.purchase_id
+		WHERE p.id = prev.id
 		  AND lower(COALESCE(p.listing_state, '')) <> $5
 		  AND (lower(COALESCE(p.listing_state, '')) <> $1 OR p.listing_client_token IS NOT NULL)
+		  AND NOT EXISTS (
+			SELECT 1 FROM purchase_history AS twin
+			WHERE twin.purchase_id = $2 AND twin.id <> p.id
+			  AND lower(COALESCE(twin.listing_state, '')) = $5
+		  )
 		RETURNING COALESCE(p.listing_id, ''), COALESCE(prev.prior_state, ''),
 		          p.listing_client_token, p.listing_price_schedule::text
 	`
@@ -2853,7 +2869,9 @@ func scanPurchaseHistoryRow(rows pgx.Rows) (PurchaseHistoryRecord, error) {
 // columns so the revoke endpoint can check idempotency without a second round
 // trip (issue #290). The marketplace columns (offering_class, listing_id,
 // listing_state) are read so the marketplace-list handler can validate
-// offering_class and look up the cloud account (issue #292).
+// offering_class and look up the cloud account (issue #292). Rows saved before
+// migration 000108 can share a purchase_id; the earliest one (created_at, then
+// id) is returned, the same row ClaimMarketplaceListingSlot claims (#267).
 func (s *PostgresStore) GetPurchaseHistoryByPurchaseID(ctx context.Context, purchaseID string) (*PurchaseHistoryRecord, error) {
 	query := `
 		SELECT account_id, purchase_id, timestamp, provider, service, region,
@@ -2863,6 +2881,7 @@ func (s *PostgresStore) GetPurchaseHistoryByPurchaseID(ctx context.Context, purc
 		       revocation_in_flight, offering_class, listing_id, listing_state
 		FROM purchase_history
 		WHERE purchase_id = $1
+		ORDER BY created_at, id
 		LIMIT 1
 	`
 	rows, err := s.db.Query(ctx, query, purchaseID)
diff --git a/internal/config/store_postgres_purchase_duplicates_integration_test.go b/internal/config/store_postgres_purchase_duplicates_integration_test.go
new file mode 100644
index 00000000..d82f384a
--- /dev/null
+++ b/internal/config/store_postgres_purchase_duplicates_integration_test.go
@@ -0,0 +1,272 @@
+//go:build integration
+// +build integration
+
+package config
+
+// Real-DB tests for purchase_history rows that share a purchase_id (#267).
+// Migration 000108 stops new duplicates, but rows saved before it may still
+// carry the same purchase_id twice, and deleting them is a pending owner
+// decision. The single-row readers and the marketplace claim must treat the
+// earliest row (created_at, then id) as the purchase, the same row the first
+// save kept, instead of whichever duplicate the planner returns first.
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/LeanerCloud/cloud-commitments-platform/internal/database/postgres/testhelpers"
+	"github.com/jackc/pgx/v5/pgxpool"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPurchaseHistoryLegacyDuplicates_Postgres(t *testing.T) {
+	ctx := context.Background()
+	// A migrated database of this test's own on the package's shared
+	// container (issue #982); it is dropped when the test ends.
+	conn := testhelpers.RequireMigratedDatabase(ctx, t, getTestMigrationsPath()).DB
+
+	store := NewPostgresStore(conn)
+	pool := conn.Pool()
+	t.Run("LookupReturnsEarliestRow", func(t *testing.T) {
+		checkLookupReturnsEarliestDuplicate(ctx, t, store, pool)
+	})
+	t.Run("ClaimRefusedWhenEarliestRowIsListed", func(t *testing.T) {
+		checkClaimHonorsListedEarliestRow(ctx, t, store, pool)
+	})
+	t.Run("ClaimRefusedWhenAnyDuplicateIsListed", func(t *testing.T) {
+		checkClaimHonorsListedTwin(ctx, t, store, pool)
+	})
+	t.Run("ClaimReportsEarliestRowState", func(t *testing.T) {
+		checkClaimReportsEarliestRowState(ctx, t, store, pool)
+	})
+	t.Run("ClaimReleaseReclaimDoesNotWedge", func(t *testing.T) {
+		checkDuplicateClaimDoesNotWedge(ctx, t, store, pool)
+	})
+	t.Run("ConcurrentClaimWaitsAndResumes", func(t *testing.T) {
+		checkConcurrentClaimOverDuplicates(ctx, t, store, pool)
+	})
+	t.Run("ParallelClaimsShareOneAttempt", func(t *testing.T) {
+		checkParallelClaimsOverDuplicates(ctx, t, store, pool)
+	})
+}
+
+// seedLegacyDuplicate saves one row for id through the store, then adds a
+// second row for the same key the way pre-000108 code did. The saved row is
+// stamped as the later one, so the earliest row is the second one on disk:
+// a lookup that does not order its rows returns the later row first.
+// It returns the earliest row's id.
+func seedLegacyDuplicate(ctx context.Context, t *testing.T, store *PostgresStore, pool *pgxpool.Pool, id string) string {
+	t.Helper()
+	require.NoError(t, store.SavePurchaseHistory(ctx, &PurchaseHistoryRecord{
+		AccountID: "acct", PurchaseID: id, Timestamp: time.Now(), Provider: "aws", Service: "ec2",
+		Region: "us-east-1", ResourceType: "t3.micro", Count: 1, Term: 3, Payment: "All Upfront",
+	}))
+	// Both timestamps predate the partial unique index's cutoff, as legacy rows do.
+	_, err := pool.Exec(ctx, `UPDATE purchase_history SET created_at = '2020-01-02T00:00:00Z' WHERE purchase_id = $1`, id)
+	require.NoError(t, err)
+	var earliest string
+	require.NoError(t, pool.QueryRow(ctx, `
+		INSERT INTO purchase_history (
+			account_id, purchase_id, timestamp, provider, service, region,
+			resource_type, count, term, payment, upfront_cost, monthly_cost,
+			estimated_savings, ramp_step, created_at)
+		SELECT account_id, purchase_id, timestamp, provider, service, region,
+		       resource_type, count, term, payment, upfront_cost, monthly_cost,
+		       estimated_savings, ramp_step, '2020-01-01T00:00:00Z'
+		FROM purchase_history WHERE purchase_id = $1
+		RETURNING id::text`, id).Scan(&earliest))
+	return earliest
+}
+
+func setRowListing(ctx context.Context, t *testing.T, pool *pgxpool.Pool, rowID, listingID, state string) {
+	t.Helper()
+	_, err := pool.Exec(ctx, `UPDATE purchase_history SET listing_id = $2, listing_state = $3 WHERE id = $1::uuid`,
+		rowID, listingID, state)
+	require.NoError(t, err)
+}
+
+func checkLookupReturnsEarliestDuplicate(ctx context.Context, t *testing.T, store *PostgresStore, pool *pgxpool.Pool) {
+	const id = "ri-dup-lookup-267"
+	earliest := seedLegacyDuplicate(ctx, t, store, pool, id)
+	setRowListing(ctx, t, pool, earliest, "ril-earliest", ListingStateCancelled)
+
+	for range 3 {
+		got, err := store.GetPurchaseHistoryByPurchaseID(ctx, id)
+		require.NoError(t, err)
+		require.NotNil(t, got)
+		assert.Equal(t, "ril-earliest", got.ListingID, "the lookup must return the earliest row, not an arbitrary duplicate")
+	}
+}
+
+// The earliest row records an active listing and a later duplicate was saved
+// without it. Claiming through the duplicate would let the handler create a
+// second AWS listing for the same RI.
+func checkClaimHonorsListedEarliestRow(ctx context.Context, t *testing.T, store *PostgresStore, pool *pgxpool.Pool) {
+	const id = "ri-dup-active-267"
+	earliest := seedLegacyDuplicate(ctx, t, store, pool, id)
+	setRowListing(ctx, t, pool, earliest, "ril-live", ListingStateActive)
+
+	claim, err := store.ClaimMarketplaceListingSlot(ctx, id, "tok-1", []byte(claimTestSchedule))
+	require.NoError(t, err)
+	assert.Nil(t, claim, "a purchase whose earliest row is listed must not be claimable")
+	assertNoPendingRows(ctx, t, pool, id)
+}
+
+// Same as above with the listing recorded on the later duplicate only.
+func checkClaimHonorsListedTwin(ctx context.Context, t *testing.T, store *PostgresStore, pool *pgxpool.Pool) {
+	const id = "ri-dup-twin-active-267"
+	earliest := seedLegacyDuplicate(ctx, t, store, pool, id)
+	_, err := pool.Exec(ctx, `UPDATE purchase_history SET listing_id = 'ril-live', listing_state = $2
+		WHERE purchase_id = $1 AND id <> $3::uuid`, id, ListingStateActive, earliest)
+	require.NoError(t, err)
+
+	claim, err := store.ClaimMarketplaceListingSlot(ctx, id, "tok-1", []byte(claimTestSchedule))
+	require.NoError(t, err)
+	assert.Nil(t, claim, "an active listing on any duplicate must block the claim")
+	assertNoPendingRows(ctx, t, pool, id)
+}
+
+func assertNoPendingRows(ctx context.Context, t *testing.T, pool *pgxpool.Pool, id string) {
+	t.Helper()
+	var pending int
+	require.NoError(t, pool.QueryRow(ctx, `SELECT count(*) FROM purchase_history WHERE purchase_id = $1 AND listing_state = $2`,
+		id, ListingStatePending).Scan(&pending))
+	assert.Zero(t, pending, "a refused claim must not leave any row pending")
+}
+
+// The claim's prior state and listing id come from the earliest row, and only
+// that row is claimed: the handler restores PriorState on release, so a value
+// taken from another duplicate, or a release that spans both, would overwrite
+// a row's recorded state with the other row's.
+func checkClaimReportsEarliestRowState(ctx context.Context, t *testing.T, store *PostgresStore, pool *pgxpool.Pool) {
+	const id = "ri-dup-prior-267"
+	earliest := seedLegacyDuplicate(ctx, t, store, pool, id)
+	setRowListing(ctx, t, pool, earliest, "ril-old", ListingStateCancelled)
+	_, err := pool.Exec(ctx, `UPDATE purchase_history SET listing_id = 'ril-twin', listing_state = $2
+		WHERE purchase_id = $1 AND id <> $3::uuid`, id, ListingStateClosed, earliest)
+	require.NoError(t, err)
+
+	claim, err := store.ClaimMarketplaceListingSlot(ctx, id, "tok-1", []byte(claimTestSchedule))
+	require.NoError(t, err)
+	require.NotNil(t, claim)
+	assert.Equal(t, ListingStateCancelled, claim.PriorState)
+	assert.Equal(t, "ril-old", claim.ListingID)
+
+	require.NoError(t, store.ReleaseMarketplaceListingClaim(ctx, id, claim.ClientToken, claim.PriorState, false))
+	var state, listingID string
+	require.NoError(t, pool.QueryRow(ctx, `SELECT COALESCE(listing_state, ''), COALESCE(listing_id, '') FROM purchase_history WHERE id = $1::uuid`,
+		earliest).Scan(&state, &listingID))
+	assert.Equal(t, ListingStateCancelled, state, "release must restore the earliest row's own state")
+	assert.Equal(t, "ril-old", listingID)
+	require.NoError(t, pool.QueryRow(ctx, `SELECT COALESCE(listing_state, ''), COALESCE(listing_id, '') FROM purchase_history WHERE purchase_id = $1 AND id <> $2::uuid`,
+		id, earliest).Scan(&state, &listingID))
+	assert.Equal(t, ListingStateClosed, state, "the claim and release must leave the other duplicate as it was")
+	assert.Equal(t, "ril-twin", listingID)
+}
+
+// The scenario from #267: identical duplicates, a claim that fails on AWS and
+// is released, then a retry. Every step must succeed and the listing, once
+// recorded, must cover every duplicate.
+func checkDuplicateClaimDoesNotWedge(ctx context.Context, t *testing.T, store *PostgresStore, pool *pgxpool.Pool) {
+	const id = "ri-dup-wedge-267"
+	seedLegacyDuplicate(ctx, t, store, pool, id)
+
+	claim, err := store.ClaimMarketplaceListingSlot(ctx, id, "tok-1", []byte(claimTestSchedule))
+	require.NoError(t, err)
+	require.NotNil(t, claim)
+	assert.False(t, claim.Resumed)
+	require.NoError(t, store.ReleaseMarketplaceListingClaim(ctx, id, claim.ClientToken, claim.PriorState, false))
+
+	claim, err = store.ClaimMarketplaceListingSlot(ctx, id, "tok-2", []byte(claimTestSchedule))
+	require.NoError(t, err)
+	require.NotNil(t, claim, "a released claim must leave the purchase claimable")
+	assert.Equal(t, "tok-2", claim.ClientToken)
+	require.NoError(t, store.UpdatePurchaseHistoryListing(ctx, id, "ril-1", ListingStateActive))
+
+	var active int
+	require.NoError(t, pool.QueryRow(ctx, `SELECT count(*) FROM purchase_history WHERE purchase_id = $1 AND listing_state = $2 AND listing_id = 'ril-1'`,
+		id, ListingStateActive).Scan(&active))
+	assert.Equal(t, 2, active, "the recorded listing must cover every duplicate")
+	claim, err = store.ClaimMarketplaceListingSlot(ctx, id, "tok-3", []byte(claimTestSchedule))
+	require.NoError(t, err)
+	assert.Nil(t, claim)
+}
+
+// Two claims race over a purchase with duplicates: the second waits for the
+// first one's lock on the earliest row and resumes its attempt.
+func checkConcurrentClaimOverDuplicates(ctx context.Context, t *testing.T, store *PostgresStore, pool *pgxpool.Pool) {
+	const id = "ri-dup-race-267"
+	earliest := seedLegacyDuplicate(ctx, t, store, pool, id)
+
+	tx, err := pool.Begin(ctx)
+	require.NoError(t, err)
+	defer func() { _ = tx.Rollback(context.Background()) }()
+	_, err = tx.Exec(ctx, `UPDATE purchase_history SET listing_state = 'pending', listing_client_token = 'tok-A',
+		listing_price_schedule = '[{"term_months":1,"price":1}]' WHERE id = $1::uuid`, earliest)
+	require.NoError(t, err)
+
+	type result struct {
+		claim *MarketplaceListingClaim
+		err   error
+	}
+	done := make(chan result, 1)
+	go func() {
+		claim, claimErr := store.ClaimMarketplaceListingSlot(ctx, id, "tok-B", []byte(`[{"term_months":2,"price":2}]`))
+		done <- result{claim, claimErr}
+	}()
+
+	require.Eventually(t, func() bool {
+		var waiting int
+		require.NoError(t, pool.QueryRow(ctx, `SELECT count(*) FROM pg_stat_activity WHERE wait_event_type = 'Lock' AND query LIKE '%listing_client_token%'`).Scan(&waiting))
+		return waiting > 0
+	}, 10*time.Second, 20*time.Millisecond, "the second claim must wait for the first claim's lock")
+	require.NoError(t, tx.Commit(ctx))
+
+	got := <-done
+	require.NoError(t, got.err)
+	require.NotNil(t, got.claim)
+	assert.True(t, got.claim.Resumed)
+	assert.Equal(t, "tok-A", got.claim.ClientToken)
+	assert.Equal(t, ListingStatePending, got.claim.PriorState)
+}
+
+// Many claims at once over a purchase with duplicates: exactly one starts a
+// fresh attempt and every other one resumes it with the same token, so the
+// handler never sends two different ClientTokens to AWS for one RI.
+func checkParallelClaimsOverDuplicates(ctx context.Context, t *testing.T, store *PostgresStore, pool *pgxpool.Pool) {
+	const id = "ri-dup-parallel-267"
+	const workers = 8
+	seedLegacyDuplicate(ctx, t, store, pool, id)
+
+	claims := make([]*MarketplaceListingClaim, workers)
+	errs := make([]error, workers)
+	start := make(chan struct{})
+	var wg sync.WaitGroup
+	for i := range workers {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			<-start
+			claims[i], errs[i] = store.ClaimMarketplaceListingSlot(ctx, id, fmt.Sprintf("tok-%d", i), []byte(claimTestSchedule))
+		}()
+	}
+	close(start)
+	wg.Wait()
+
+	fresh := 0
+	tokens := map[string]bool{}
+	for i := range workers {
+		require.NoError(t, errs[i])
+		require.NotNil(t, claims[i])
+		if !claims[i].Resumed {
+			fresh++
+		}
+		tokens[claims[i].ClientToken] = true
+	}
+	assert.Equal(t, 1, fresh, "exactly one claim starts the attempt")
+	assert.Len(t, tokens, 1, "every claim must carry the same token")
+}