diff --git a/packages/shared/src/pulse/service.test.ts b/packages/shared/src/pulse/service.test.ts
index 8b51eaf4..631201bc 100644
--- a/packages/shared/src/pulse/service.test.ts
+++ b/packages/shared/src/pulse/service.test.ts
@@ -194,12 +194,15 @@ async function makeService(
 }
 
 const PORTFOLIO: PortfolioSnapshot = {
+  // Single-currency book: an unconverted `marketValue` is only comparable with
+  // `totalAssets` when the holding currency and the base currency are known.
+  baseCurrency: 'USD',
   totalAssets: 10_000,
   accounts: [],
   holdings: [
-    { symbol: 'AAPL.US', name: 'Apple', marketValueBase: 1_500, marketValue: 1_500 },
-    { symbol: 'MSFT.US', name: 'Microsoft', marketValue: 2_500 },
-    { symbol: 'GOOGL.US', name: 'Alphabet', marketValueBase: 4_000 },
+    { symbol: 'AAPL.US', name: 'Apple', currency: 'USD', marketValueBase: 1_500, marketValue: 1_500 },
+    { symbol: 'MSFT.US', name: 'Microsoft', currency: 'USD', marketValue: 2_500 },
+    { symbol: 'GOOGL.US', name: 'Alphabet', currency: 'USD', marketValueBase: 4_000 },
   ],
   fetchedAt: NOW_MS,
 }
@@ -280,6 +283,55 @@ describe('portfolioExposurePercent', () => {
     expect(portfolioExposurePercent('AAPL.US')).toBeUndefined()
     expect(portfolioExposurePercent('AAPL.US', { ...PORTFOLIO, totalAssets: undefined })).toBeUndefined()
   })
+
+  it('does not divide an unconverted marketValue by a base-currency total', () => {
+    // 780,000 HKD is NOT 780% of a 100,000 USD book — without a converted
+    // marketValueBase the exposure is simply unknown.
+    const crossCurrency: PortfolioSnapshot = {
+      baseCurrency: 'USD',
+      totalAssets: 100_000,
+      accounts: [],
+      holdings: [
+        { symbol: '0700.HK', name: 'Tencent', currency: 'HKD', marketValue: 780_000 },
+      ],
+      fetchedAt: NOW_MS,
+    }
+    expect(portfolioExposurePercent('0700.HK', crossCurrency)).toBeUndefined()
+  })
+
+  it('uses marketValue when the holding currency matches the base currency', () => {
+    const sameCurrency: PortfolioSnapshot = {
+      baseCurrency: 'HKD',
+      totalAssets: 1_000_000,
+      accounts: [],
+      holdings: [
+        { symbol: '0700.HK', name: 'Tencent', currency: 'HKD', marketValue: 780_000 },
+      ],
+      fetchedAt: NOW_MS,
+    }
+    expect(portfolioExposurePercent('0700.HK', sameCurrency)).toBe(78)
+  })
+
+  it('leaves exposure undefined when either currency is unknown', () => {
+    // With the holding currency (or the base currency) missing, the unit of the
+    // denominator is unverifiable, so the raw market value cannot stand in —
+    // same rule as evaluatePositionWeight in the alerts evaluator.
+    const noHoldingCurrency: PortfolioSnapshot = {
+      baseCurrency: 'USD',
+      totalAssets: 100_000,
+      accounts: [],
+      holdings: [{ symbol: '0700.HK', name: 'Tencent', marketValue: 780_000 }],
+      fetchedAt: NOW_MS,
+    }
+    const noBaseCurrency: PortfolioSnapshot = {
+      totalAssets: 100_000,
+      accounts: [],
+      holdings: [{ symbol: '0700.HK', name: 'Tencent', currency: 'HKD', marketValue: 780_000 }],
+      fetchedAt: NOW_MS,
+    }
+    expect(portfolioExposurePercent('0700.HK', noHoldingCurrency)).toBeUndefined()
+    expect(portfolioExposurePercent('0700.HK', noBaseCurrency)).toBeUndefined()
+  })
 })
 
 describe('computePersonalImpact', () => {
diff --git a/packages/shared/src/pulse/service.ts b/packages/shared/src/pulse/service.ts
index efbe2cbe..4879d187 100644
--- a/packages/shared/src/pulse/service.ts
+++ b/packages/shared/src/pulse/service.ts
@@ -1,5 +1,6 @@
 import type {
   CapabilityRegistry,
+  Holding,
   MarketStatus,
   MarketTemperature,
   PortfolioSnapshot,
@@ -303,6 +304,31 @@ export function computePersonalImpact(
   return { scope: 'watchlist', items }
 }
 
+/**
+ * Market value of `holding` that is safe to divide by a base-currency total.
+ *
+ * `marketValueBase` is the vendor-converted base-currency value and is always
+ * safe. `marketValue` is denominated in `holding.currency` (see core
+ * `Holding`), so it may only stand in when the two currencies are known to
+ * match — otherwise dividing it by `PortfolioSnapshot.totalAssets` would scale
+ * the exposure by the FX rate. This mirrors `evaluatePositionWeight` in the
+ * alerts evaluator.
+ */
+function baseCurrencyValue(holding: Holding, baseCurrency?: string): number | undefined {
+  const converted = toFiniteNumber(holding.marketValueBase)
+  if (converted !== undefined) return converted
+  const raw = toFiniteNumber(holding.marketValue)
+  if (raw === undefined) return undefined
+  // `sameCurrency` must be false when either side is unknown — an unconverted
+  // `marketValue` divided by a base-currency total is only meaningful when both
+  // currencies are known to be the same one (mirrors evaluatePositionWeight).
+  const holdingCurrency = holding.currency?.trim().toUpperCase()
+  const base = baseCurrency?.trim().toUpperCase()
+  const sameCurrency = Boolean(holdingCurrency && base && holdingCurrency === base)
+  if (!sameCurrency) return undefined
+  return raw
+}
+
 /** Holding market value as a share of portfolio total assets (%), when computable. */
 export function portfolioExposurePercent(
   symbol: string,
@@ -314,7 +340,7 @@ export function portfolioExposurePercent(
   const target = normalizeSymbol(symbol)
   for (const holding of portfolio.holdings) {
     if (normalizeSymbol(holding.symbol) !== target) continue
-    const weight = holding.marketValueBase ?? holding.marketValue
+    const weight = baseCurrencyValue(holding, portfolio.baseCurrency)
     if (weight === undefined || !Number.isFinite(weight)) return undefined
     return round2((weight / total) * 100)
   }