diff --git a/crates/bindings-typescript/src/server/runtime.ts b/crates/bindings-typescript/src/server/runtime.ts
index 70c6eb81401..a817e2616c0 100644
--- a/crates/bindings-typescript/src/server/runtime.ts
+++ b/crates/bindings-typescript/src/server/runtime.ts
@@ -1195,9 +1195,18 @@ export function makeTableView(
     const numColumns = column_ids.length;
 
     const columnSet = new Set(column_ids);
+    // An index is unique only if its columns are exactly a unique constraint's
+    // columns. A proper subset is not: a prefix of a composite unique
+    // constraint can match many rows, so it needs the ranged accessors.
     const isUnique = table.constraints
       .filter(x => x.data.tag === 'Unique')
-      .some(x => columnSet.isSubsetOf(new Set(x.data.value.columns)));
+      .some(x => {
+        const constraintColumns = new Set(x.data.value.columns);
+        return (
+          columnSet.size === constraintColumns.size &&
+          [...columnSet].every(column => constraintColumns.has(column))
+        );
+      });
 
     const isPrimaryKey =
       isUnique &&
diff --git a/crates/bindings-typescript/tests/index_unique_exact_columns.test.ts b/crates/bindings-typescript/tests/index_unique_exact_columns.test.ts
new file mode 100644
index 00000000000..89a1c273e2d
--- /dev/null
+++ b/crates/bindings-typescript/tests/index_unique_exact_columns.test.ts
@@ -0,0 +1,186 @@
+import { describe, expect, it, vi } from 'vitest';
+
+// `runtime.ts` and `procedures.ts` form an import cycle (procedures extends
+// runtime's ReducerCtxImpl). Vitest's loader evaluates the cycle in an order
+// that leaves the base class undefined. runtime only needs `callProcedure`, and
+// not on the table-view path under test, so stub procedures to break the cycle.
+vi.mock('../src/server/procedures', () => ({
+  callProcedure: () => {
+    throw new Error('callProcedure is not stubbed for this test');
+  },
+}));
+
+// A host stub that can actually hand rows back, so a scan can be observed
+// returning more than one row. `runtime.ts` builds its `sys` object by
+// spreading both syscall modules at import time, so both have to be mocked.
+const host = vi.hoisted(() => ({
+  pointScans: 0,
+  rangeScans: 0,
+  /** BSATN for the rows the next iterator yields, concatenated. */
+  rows: new Uint8Array(),
+  exhausted: false,
+  reset(rows: Uint8Array) {
+    host.pointScans = 0;
+    host.rangeScans = 0;
+    host.rows = rows;
+    host.exhausted = false;
+  },
+  overrides: {
+    datastore_index_scan_range_bsatn: (): number => {
+      host.rangeScans += 1;
+      return 1;
+    },
+    datastore_index_scan_point_bsatn: (): number => {
+      host.pointScans += 1;
+      return 1;
+    },
+    // `> 0` means "yielded rows, more to come", `< 0` means "yielded rows and
+    // is now exhausted", `0` means "empty". One chunk holds every row here.
+    row_iter_bsatn_advance: (_iter: number, buffer: ArrayBuffer): number => {
+      if (host.exhausted) return 0;
+      host.exhausted = true;
+      new Uint8Array(buffer).set(host.rows);
+      return -host.rows.length;
+    },
+  },
+}));
+
+vi.mock('spacetime:sys@2.0', async importOriginal => ({
+  ...(await importOriginal<object>()),
+  ...host.overrides,
+}));
+vi.mock('spacetime:sys@2.1', async importOriginal => ({
+  ...(await importOriginal<object>()),
+  ...host.overrides,
+}));
+
+import { AlgebraicType } from '../src/lib/algebraic_type';
+import BinaryWriter from '../src/lib/binary_writer';
+import type { ConstraintOpts } from '../src/lib/constraints';
+import { ModuleContext } from '../src/lib/schema';
+import { table } from '../src/lib/table';
+import { t } from '../src/lib/type_builders';
+import { Range } from '../src/server/range';
+import { makeTableView } from '../src/server/runtime';
+
+type MembershipRow = { id: bigint; tenant: string; email: string };
+
+/**
+ * A table whose unique constraint covers two columns, with a btree index on a
+ * proper subset of them (`tenant`) alongside one that matches the constraint
+ * exactly (`tenant, email`).
+ *
+ * `ConstraintOpts` currently types `columns` as a one-column tuple, so the
+ * composite constraint is spelled out through the raw constraint shape. Every
+ * layer underneath already handles N columns: `table()` maps over
+ * `constraintOpts.columns`, `RawConstraintDefV10`'s `Unique` payload is a
+ * column list, and `crates/codegen` emits multi-column unique constraints.
+ */
+function membershipTable() {
+  const ctx = new ModuleContext();
+  const membership = table(
+    {
+      name: 'membership',
+      indexes: [
+        {
+          accessor: 'byTenant',
+          name: 'membership_tenant_idx_btree',
+          algorithm: 'btree',
+          columns: ['tenant'] as const,
+        },
+        {
+          accessor: 'byTenantEmail',
+          name: 'membership_tenant_email_idx_btree',
+          algorithm: 'btree',
+          columns: ['tenant', 'email'] as const,
+        },
+      ] as const,
+      constraints: [
+        {
+          name: 'membership_tenant_email_key',
+          constraint: 'unique',
+          columns: ['tenant', 'email'],
+        },
+      ] as unknown as ConstraintOpts<'id' | 'tenant' | 'email'>[],
+    },
+    {
+      id: t.u64().primaryKey().autoInc(),
+      tenant: t.string(),
+      email: t.string(),
+    }
+  );
+
+  const rawTableDef = membership.tableDef(ctx, 'membership');
+  const view = makeTableView(ctx.typespace, rawTableDef) as any;
+  const rowType = ctx.typespace.types[rawTableDef.productTypeRef];
+  const serializeRow = AlgebraicType.makeSerializer(rowType, ctx.typespace);
+
+  const encodeRows = (rows: MembershipRow[]): Uint8Array => {
+    const writer = new BinaryWriter(1024);
+    for (const row of rows) serializeRow(writer, row);
+    return writer.getBuffer();
+  };
+
+  return { view, encodeRows };
+}
+
+describe('index uniqueness is decided by an exact column match', () => {
+  it('leaves a btree index on a prefix of a composite unique constraint ranged', () => {
+    const { view, encodeRows } = membershipTable();
+    const rows: MembershipRow[] = [
+      { id: 1n, tenant: 'acme', email: 'ada@acme.test' },
+      { id: 2n, tenant: 'acme', email: 'grace@acme.test' },
+    ];
+
+    // `tenant` alone is not unique: two rows share it, so the index has to be
+    // the ranged kind that can return all of them.
+    expect(view.byTenant.filter).toBeInstanceOf(Function);
+    expect(view.byTenant.find).toBeUndefined();
+
+    host.reset(encodeRows(rows));
+    expect([...view.byTenant.filter('acme')]).toEqual(rows);
+    expect(host.pointScans).toBe(1);
+
+    // A ranged index also has to accept a `Range` and take the range-scan path.
+    host.reset(encodeRows(rows));
+    const range = new Range<string>(
+      { tag: 'included', value: 'acme' },
+      { tag: 'excluded', value: 'zenith' }
+    );
+    expect([...view.byTenant.filter(range)]).toEqual(rows);
+    expect(host.rangeScans).toBe(1);
+  });
+
+  it('keeps the index matching the composite unique constraint unique', () => {
+    const { view, encodeRows } = membershipTable();
+    const row: MembershipRow = {
+      id: 1n,
+      tenant: 'acme',
+      email: 'ada@acme.test',
+    };
+
+    expect(view.byTenantEmail.find).toBeInstanceOf(Function);
+    expect(view.byTenantEmail.filter).toBeUndefined();
+
+    host.reset(encodeRows([row]));
+    expect(view.byTenantEmail.find(['acme', 'ada@acme.test'])).toEqual(row);
+    expect(host.pointScans).toBe(1);
+  });
+
+  it('keeps the primary-key index unique and updatable', () => {
+    const { view, encodeRows } = membershipTable();
+    const row: MembershipRow = {
+      id: 1n,
+      tenant: 'acme',
+      email: 'ada@acme.test',
+    };
+
+    expect(view.id.find).toBeInstanceOf(Function);
+    expect(view.id.update).toBeInstanceOf(Function);
+    expect(view.id.filter).toBeUndefined();
+
+    host.reset(encodeRows([row]));
+    expect(view.id.find(1n)).toEqual(row);
+    expect(host.pointScans).toBe(1);
+  });
+});