diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Certificates/CertificateStoreManager.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Certificates/CertificateStoreManager.cs
index 15180c94..fb0f7cc6 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Certificates/CertificateStoreManager.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Certificates/CertificateStoreManager.cs
@@ -102,7 +102,7 @@ public sealed class CertificateStoreManager
     // store mutation stays synchronous. Every return path (success + every failure) is audited
     // because Trust/Untrust/Delete each route their single result through here.
     private void Audit(string action, string store, string thumbprint, string actor, CertActionResult r)
-        => _audit.WriteAsync(CertAuditEvents.Build(action, store, thumbprint, actor, r.Success, r.Error));
+        => _ = _audit.WriteAsync(CertAuditEvents.Build(action, store, thumbprint, actor, r.Success, r.Error));
 
     private CertActionResult Move(string fromSub, string toSub, string thumbprint)
     {
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Certificates/CertificateStoreManagerTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Certificates/CertificateStoreManagerTests.cs
index 3e9ecd1b..c08ed655 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Certificates/CertificateStoreManagerTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Certificates/CertificateStoreManagerTests.cs
@@ -288,4 +288,19 @@ public sealed class CertificateStoreManagerTests : IDisposable
         evt.SourceNode.ShouldBe(absent);
         evt.Actor.ShouldBe("bob");
     }
+
+    [Fact]
+    public void Untrust_not_found_writes_one_failure_audit_event()
+    {
+        var absent = new string('0', 40);
+
+        var result = _sut.Untrust(absent, "erin");
+
+        result.Success.ShouldBeFalse();
+        var evt = _audit.Events.ShouldHaveSingleItem();
+        evt.Action.ShouldBe("Untrust");
+        evt.Outcome.ShouldBe(ZB.MOM.WW.Audit.AuditOutcome.Failure);
+        evt.SourceNode.ShouldBe(absent);
+        evt.Actor.ShouldBe("erin");
+    }
 }