diff --git a/app/schemas/purchaseorderline.schema.js b/app/schemas/purchaseorderline.schema.js
index 8e424fa..397275c 100644
--- a/app/schemas/purchaseorderline.schema.js
+++ b/app/schemas/purchaseorderline.schema.js
@@ -8,11 +8,30 @@ const intIdParam = z.object({
     id: z.coerce.number().int().positive(),
 });
 
+// PO-line quantity + per-unit price. Both are stored as Sequelize
+// DOUBLE columns. zod's `.number()` rejects NaN by default but lets
+// `Infinity` / `-Infinity` slip through — and the coerce path turns
+// the string `"Infinity"` into the float. An `inf` in either column
+// would silently corrupt every downstream calculation (PO totals,
+// inventory valuation, reconciliation reports). Pin both to finite
+// real numbers at the boundary.
+//
+// Zero and negative values still pass — a $0 line is a real "freebie
+// included with order" case; a negative line can be used for an
+// inline credit/discount entry on the PO. Mirrors the cpayAmount /
+// injbAmount validators (#172 / #180).
+const polQtyField = z.coerce.number().finite({
+    message: 'polQty must be a finite number.',
+});
+const polPriceField = z.coerce.number().finite({
+    message: 'polPrice must be a finite number.',
+});
+
 const createBody = z.object({
     polpoh: z.coerce.number().int().positive(),
     polItemDesc: z.string().min(1).max(1000),
-    polQty: z.coerce.number(),
-    polPrice: z.coerce.number(),
+    polQty: polQtyField,
+    polPrice: polPriceField,
     polInvtId: z.coerce.number().int().positive(),
 }).strict({
     message: 'Unexpected field in body. Whitelist: polpoh, polItemDesc, polQty, polPrice, polInvtId.',
@@ -20,8 +39,8 @@ const createBody = z.object({
 
 const updateBody = z.object({
     polItemDesc: z.string().min(1).max(1000).optional(),
-    polQty: z.coerce.number().optional(),
-    polPrice: z.coerce.number().optional(),
+    polQty: polQtyField.optional(),
+    polPrice: polPriceField.optional(),
     polInvtId: z.coerce.number().int().positive().optional(),
 }).strict({
     message: 'Unexpected field in body. Whitelist: polItemDesc, polQty, polPrice, polInvtId.',
diff --git a/tests/api/purchaseorderline.test.js b/tests/api/purchaseorderline.test.js
index 6d56f60..bbd86f8 100644
--- a/tests/api/purchaseorderline.test.js
+++ b/tests/api/purchaseorderline.test.js
@@ -64,4 +64,41 @@ describe('PurchaseOrderLine body validation', () => {
         });
         expect(res.status).toBe(400);
     });
+
+    test('POST rejects non-finite polQty (string "Infinity" coerces to the float)', async () => {
+        const res = await request(app).post('/v1/purchaseorderline').set('authKey', 'any').send({
+            polpoh: 1, polItemDesc: 'Widget', polQty: 'Infinity', polPrice: 5, polInvtId: 1,
+        });
+        expect(res.status).toBe(400);
+    });
+
+    test('POST rejects non-finite polPrice', async () => {
+        const res = await request(app).post('/v1/purchaseorderline').set('authKey', 'any').send({
+            polpoh: 1, polItemDesc: 'Widget', polQty: 10, polPrice: '-Infinity', polInvtId: 1,
+        });
+        expect(res.status).toBe(400);
+    });
+
+    test('POST accepts zero polQty / polPrice (freebie line)', async () => {
+        // A $0 PO line is a real "free sample included" case; pin
+        // that the .finite() refinement doesn't accidentally block 0.
+        const res = await request(app).post('/v1/purchaseorderline').set('authKey', 'any').send({
+            polpoh: 1, polItemDesc: 'Freebie', polQty: 0, polPrice: 0, polInvtId: 1,
+        });
+        expect(res.status).not.toBe(400);
+    });
+
+    test('POST accepts negative polQty / polPrice (inline credit / discount)', async () => {
+        const res = await request(app).post('/v1/purchaseorderline').set('authKey', 'any').send({
+            polpoh: 1, polItemDesc: 'Volume discount', polQty: -1, polPrice: -10, polInvtId: 1,
+        });
+        expect(res.status).not.toBe(400);
+    });
+
+    test('PATCH rejects non-finite polPrice', async () => {
+        const res = await request(app).patch('/v1/purchaseorderline/1').set('authKey', 'any').send({
+            polPrice: 'Infinity',
+        });
+        expect(res.status).toBe(400);
+    });
 });