diff --git a/src/prices/__tests__/is-variable-price.test.ts b/src/prices/__tests__/is-variable-price.test.ts
index 5e122c1..dacae83 100644
--- a/src/prices/__tests__/is-variable-price.test.ts
+++ b/src/prices/__tests__/is-variable-price.test.ts
@@ -54,7 +54,28 @@ describe('isVariablePrice', () => {
     expect(isVariablePrice(makePrice({ pricing_model: 'external_getag' }))).toBe(false);
   });
 
-  it('returns false for CompositePrice', () => {
+  it('returns true for undefined pricing_model with variable_price true', () => {
+    expect(isVariablePrice({ variable_price: true } as Price)).toBe(true);
+  });
+
+  it('returns false for undefined pricing_model with variable_price false', () => {
+    expect(isVariablePrice({ variable_price: false } as Price)).toBe(false);
+  });
+
+  it('returns true for null pricing_model with variable_price true', () => {
+    expect(isVariablePrice({ pricing_model: null, variable_price: true } as unknown as Price)).toBe(true);
+  });
+  it('returns false for null pricing_model with variable_price false', () => {
+    expect(isVariablePrice({ pricing_model: null, variable_price: false } as unknown as Price)).toBe(false);
+  });
+
+  it('returns false for CompositePrice with is_composite_price', () => {
+    const composite = { is_composite_price: true, price_components: [] } as unknown as CompositePrice;
+
+    expect(isVariablePrice(composite)).toBe(false);
+  });
+
+  it('returns false for CompositePrice with price_components array', () => {
     const composite = { price_components: [makePrice()] } as unknown as CompositePrice;
 
     expect(isVariablePrice(composite)).toBe(false);
diff --git a/src/prices/is-variable-price.ts b/src/prices/is-variable-price.ts
index a28ec33..e076b5c 100644
--- a/src/prices/is-variable-price.ts
+++ b/src/prices/is-variable-price.ts
@@ -10,21 +10,24 @@ const isTieredPrice = (price: Price): boolean => {
 };
 
 export const isVariablePrice = (price: Price | CompositePrice): boolean => {
-  if (price.is_composite_price) {
-    return false;
-  }
+  if (price.is_composite_price || Array.isArray(price.price_components)) return false;
 
   const p = price as Price;
+  const { pricing_model, get_ag, variable_price } = p;
+
+  if (isTieredPrice(p) || pricing_model === PricingModel.dynamicTariff) return true;
+
+  if (pricing_model === PricingModel.externalGetAG) {
+    return (
+      get_ag?.type === TypeGetAg.workPrice ||
+      (get_ag?.type === TypeGetAg.basePrice && get_ag?.markup_pricing_model === MarkupPricingModel.tieredFlatFee)
+    );
+  }
 
-  if (isTieredPrice(p)) return true;
-  if (p.pricing_model === PricingModel.dynamicTariff) return true;
-  if (p.pricing_model === PricingModel.externalGetAG) {
-    if (p.get_ag?.type === TypeGetAg.workPrice) return true;
-    if (p.get_ag?.type === TypeGetAg.basePrice && p.get_ag?.markup_pricing_model === MarkupPricingModel.tieredFlatFee) {
-      return true;
-    }
+  // We treat undefined or null pricing_model as perUnit
+  if (pricing_model === PricingModel.perUnit || !pricing_model) {
+    return Boolean(variable_price);
   }
-  if (p.pricing_model === PricingModel.perUnit && p.variable_price) return true;
 
   return false;
 };