diff --git a/app/schemas/inventoryitem.schema.js b/app/schemas/inventoryitem.schema.js
index db83f13..e55f1ed 100644
--- a/app/schemas/inventoryitem.schema.js
+++ b/app/schemas/inventoryitem.schema.js
@@ -8,9 +8,25 @@ const intIdParam = z.object({
     id: z.coerce.number().int().positive(),
 });
 
+// `invitQty` is the on-hand inventory quantity stored as a Sequelize
+// DOUBLE column. zod's `.number()` rejects NaN by default but allows
+// `Infinity` / `-Infinity` — and the coerce path turns the string
+// `"Infinity"` into the float. An `inf` qty silently corrupts every
+// downstream consumer that does arithmetic against it (PO line
+// receiving, inventory-transaction net-position, valuation reports).
+//
+// Add `.finite()` at the boundary. Zero stays valid (a stocked item
+// momentarily at 0 on-hand) and negatives stay valid (backorders, or
+// historical fractional reconciliation entries that some accounting
+// flows allow). Mirrors the polQtyField / polPriceField validators
+// from #194 and btHourlyRateField from #206.
+const invitQtyField = z.coerce.number().finite({
+    message: 'invitQty must be a finite number.',
+});
+
 const createInventoryItemBody = z.object({
     invitDescription: z.string().min(1).max(1000),
-    invitQty: z.coerce.number(),
+    invitQty: invitQtyField,
     invitCompId: z.coerce.number().int().positive().optional(),
 }).strict({
     message: 'Unexpected field in body. Whitelist: invitDescription, invitQty, invitCompId.',
@@ -18,7 +34,7 @@ const createInventoryItemBody = z.object({
 
 const updateInventoryItemBody = z.object({
     invitDescription: z.string().min(1).max(1000).optional(),
-    invitQty: z.coerce.number().optional(),
+    invitQty: invitQtyField.optional(),
 }).strict({
     message: 'Unexpected field in body. Whitelist: invitDescription, invitQty.',
 });
diff --git a/tests/api/inventoryitem.test.js b/tests/api/inventoryitem.test.js
index ee92d1c..e5cbfe6 100644
--- a/tests/api/inventoryitem.test.js
+++ b/tests/api/inventoryitem.test.js
@@ -75,6 +75,40 @@ describe('InventoryItem body validation', () => {
             .send({ invitDescription: 'X' });
         expect(res.status).toBe(400);
     });
+
+    test('POST rejects non-finite invitQty (string "Infinity" coerces to the float)', async () => {
+        const res = await request(app)
+            .post('/v1/inventoryitem')
+            .set('authKey', 'any')
+            .send({ invitDescription: 'Widget', invitQty: 'Infinity' });
+        expect(res.status).toBe(400);
+    });
+
+    test('POST accepts zero invitQty (item at 0 on-hand)', async () => {
+        // Pin that the .finite() guard doesn't accidentally block 0 —
+        // an item momentarily out of stock should still be modelable.
+        const res = await request(app)
+            .post('/v1/inventoryitem')
+            .set('authKey', 'any')
+            .send({ invitDescription: 'Widget', invitQty: 0 });
+        expect(res.status).not.toBe(400);
+    });
+
+    test('POST accepts negative invitQty (backorder / reconciliation entries)', async () => {
+        const res = await request(app)
+            .post('/v1/inventoryitem')
+            .set('authKey', 'any')
+            .send({ invitDescription: 'Backorder', invitQty: -3 });
+        expect(res.status).not.toBe(400);
+    });
+
+    test('PATCH rejects -Infinity invitQty', async () => {
+        const res = await request(app)
+            .patch('/v1/inventoryitem/1')
+            .set('authKey', 'any')
+            .send({ invitQty: '-Infinity' });
+        expect(res.status).toBe(400);
+    });
 });
 
 describe('InventoryItem tenant-enumeration defense (secure 404)', () => {