diff --git a/src/dotnet/QuantEngine.Application/Services/FactorComputationService.cs b/src/dotnet/QuantEngine.Application/Services/FactorComputationService.cs
index b93fac1d..9e783669 100644
--- a/src/dotnet/QuantEngine.Application/Services/FactorComputationService.cs
+++ b/src/dotnet/QuantEngine.Application/Services/FactorComputationService.cs
@@ -42,6 +42,10 @@ public sealed class FactorComputationService
         FactorOutputs outputs,
         DateTimeOffset? observedAt = null)
     {
+        ticker = RequireValue(ticker, nameof(ticker));
+        sourceVersion = RequireValue(sourceVersion, nameof(sourceVersion));
+        ArgumentNullException.ThrowIfNull(outputs);
+
         var when = observedAt ?? DateTimeOffset.UtcNow;
         await _history.AppendFactorOutputAsync("momentum_20d", sourceVersion, outputs.Momentum20D, "PASS", sourceVersion, when);
         await _history.AppendFactorOutputAsync("momentum_60d", sourceVersion, outputs.Momentum60D, "PASS", sourceVersion, when);
@@ -52,4 +56,14 @@ public sealed class FactorComputationService
         await _history.AppendFactorOutputAsync("rs_20d", sourceVersion, outputs.Rs20D, "PASS", sourceVersion, when);
         _auditTrail.Append("factor_audit", ticker, new FactorComputationAudit(ticker, 0, 0, "PERSISTED", when, sourceVersion));
     }
+
+    private static string RequireValue(string value, string parameterName)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            throw new ArgumentException("Value is required.", parameterName);
+        }
+
+        return value.Trim();
+    }
 }
diff --git a/src/dotnet/QuantEngine.Core.Tests/FactorComputationServiceTests.cs b/src/dotnet/QuantEngine.Core.Tests/FactorComputationServiceTests.cs
index d536a086..42311b66 100644
--- a/src/dotnet/QuantEngine.Core.Tests/FactorComputationServiceTests.cs
+++ b/src/dotnet/QuantEngine.Core.Tests/FactorComputationServiceTests.cs
@@ -29,4 +29,16 @@ public class FactorComputationServiceTests
         storeMock.Verify(s => s.AppendAsync("factor_output_history", It.IsAny<IDictionary<string, object?>>()), Times.Exactly(7));
         auditTrailMock.Verify(a => a.Append("factor_audit", "005930", It.IsAny<FactorComputationAudit>()), Times.Once);
     }
+
+    [Fact]
+    public async Task AppendFactorOutputsAsync_RejectsBlankTicker()
+    {
+        var storeMock = new Mock<IPostgresqlHistoryStore>();
+        var auditTrailMock = new Mock<IRuntimeAuditTrailService>();
+        var history = new HistoryIngestionService(storeMock.Object);
+        var service = new FactorComputationService(history, auditTrailMock.Object);
+
+        await Assert.ThrowsAsync<ArgumentException>(() =>
+            service.AppendFactorOutputsAsync("  ", "v1", new FactorOutputs(1, 2, 3, 4, 5, 6, 7)));
+    }
 }