diff --git a/app/Services/CurrencyConversionService.php b/app/Services/CurrencyConversionService.php
index 8dfa2997..94673b04 100644
--- a/app/Services/CurrencyConversionService.php
+++ b/app/Services/CurrencyConversionService.php
@@ -86,6 +86,11 @@ class CurrencyConversionService
             foreach ($this->rateUrls($currency, $candidateDate) as $url) {
                 try {
                     $response = Http::timeout(10)->get($url);
+
+                    if ($response->notFound()) {
+                        continue;
+                    }
+
                     $response->throw();
 
                     return $response->json($currency) ?? [];
@@ -95,7 +100,16 @@ class CurrencyConversionService
             }
         }
 
-        throw new RuntimeException("Failed to fetch currency rates for {$currency} on {$date}: {$lastException?->getMessage()}", 0, $lastException);
+        if ($lastException !== null) {
+            throw new RuntimeException("Failed to fetch currency rates for {$currency} on {$date}: {$lastException->getMessage()}", 0, $lastException);
+        }
+
+        Log::warning('Currency rates unavailable, all sources returned 404', [
+            'currency' => $currency,
+            'date' => $date,
+        ]);
+
+        return [];
     }
 
     /**
diff --git a/tests/Feature/CurrencyConversionServiceTest.php b/tests/Feature/CurrencyConversionServiceTest.php
index 94067c47..aa3581c2 100644
--- a/tests/Feature/CurrencyConversionServiceTest.php
+++ b/tests/Feature/CurrencyConversionServiceTest.php
@@ -73,6 +73,18 @@ test('throws when both primary and fallback fail', function () {
     $service->convert('BTC', 'EUR', 1.0, '2026-01-15');
 })->throws(RuntimeException::class);
 
+test('returns zero when base currency is unknown and all sources return 404', function () {
+    Http::fake([
+        'cdn.jsdelivr.net/*' => Http::response('Not Found', 404),
+        'currency-api.pages.dev/*' => Http::response('Not Found', 404),
+    ]);
+
+    $service = new CurrencyConversionService;
+    $result = $service->convert('BTC', 'XXX', 1.0, '2026-01-15');
+
+    expect($result)->toBe(0.0);
+});
+
 test('falls back to previous historical date when requested release is missing', function () {
     Http::fake([
         'cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@2025-12-10/*' => Http::response('Not Found', 404),