diff --git a/csharp/autobuilder/Semmle.Autobuild.Shared/Autobuilder.cs b/csharp/autobuilder/Semmle.Autobuild.Shared/Autobuilder.cs
index 3e9a4952645..685f9752a2f 100644
--- a/csharp/autobuilder/Semmle.Autobuild.Shared/Autobuilder.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.Shared/Autobuilder.cs
@@ -322,16 +322,30 @@ namespace Semmle.Autobuild.Shared
                 .Select(result => result.ToDiagnosticMessage(this, diagSeverity))
                 .ForEach(AddDiagnostic);
 
-            if (buildResult == 0 && IsBuildless)
+            if (IsBuildless)
             {
-                AddDiagnostic(new DiagnosticMessage(
-                    Options.Language,
-                    "buildless/complete",
-                    "C# analysis with build-mode 'none' completed",
-                    visibility: new DiagnosticMessage.TspVisibility(statusPage: false, cliSummaryTable: true, telemetry: true),
-                    markdownMessage: "C# analysis with build-mode 'none' completed.",
-                    severity: DiagnosticMessage.TspSeverity.Unknown
-                ));
+                if (buildResult == 0)
+                {
+                    AddDiagnostic(new DiagnosticMessage(
+                        Options.Language,
+                        "buildless/complete",
+                        "C# analysis with build-mode 'none' completed",
+                        visibility: new DiagnosticMessage.TspVisibility(statusPage: false, cliSummaryTable: true, telemetry: true),
+                        markdownMessage: "C# analysis with build-mode 'none' completed.",
+                        severity: DiagnosticMessage.TspSeverity.Unknown
+                    ));
+                }
+                else
+                {
+                    AddDiagnostic(new DiagnosticMessage(
+                        Options.Language,
+                        "buildless/failed",
+                        "C# analysis with build-mode 'none' failed",
+                        visibility: new DiagnosticMessage.TspVisibility(statusPage: true, cliSummaryTable: true, telemetry: true),
+                        markdownMessage: "C# analysis with build-mode 'none' failed.",
+                        severity: DiagnosticMessage.TspSeverity.Error
+                    ));
+                }
             }
 
             return buildResult;
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs
index c4c901a3cc4..713d52d8e3f 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs
@@ -728,6 +728,11 @@ namespace Semmle.Extraction.CSharp.DependencyFetching
         /// </summary>
         public IEnumerable<string> GeneratedSourceFiles => generatedSources;
 
+        /// <summary>
+        /// All of the non-generated source files in the source directory.
+        /// </summary>
+        public IEnumerable<string> NonGeneratedSourcesFiles => nonGeneratedSources;
+
         /// <summary>
         /// All of the source files in the source directory.
         /// </summary>
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.Standalone/Extractor.cs b/csharp/extractor/Semmle.Extraction.CSharp.Standalone/Extractor.cs
index d868768e350..9a58011196c 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.Standalone/Extractor.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.Standalone/Extractor.cs
@@ -146,7 +146,7 @@ namespace Semmle.Extraction.CSharp.Standalone
             logger.Log(Severity.Info, "Extracting C# in buildless mode");
             using var dependencyManager = new DependencyManager(options.SrcDir, logger);
 
-            if (!dependencyManager.AllSourceFiles.Any())
+            if (!dependencyManager.NonGeneratedSourcesFiles.Any())
             {
                 logger.Log(Severity.Error, "No source files found");
                 return ExitCode.Errors;
diff --git a/csharp/ql/integration-tests/all-platforms/standalone_failed/diagnostics.expected b/csharp/ql/integration-tests/all-platforms/standalone_failed/diagnostics.expected
new file mode 100644
index 00000000000..65b8c89ce70
--- /dev/null
+++ b/csharp/ql/integration-tests/all-platforms/standalone_failed/diagnostics.expected
@@ -0,0 +1,28 @@
+{
+  "markdownMessage": "C# analysis with build-mode 'none' failed.",
+  "severity": "error",
+  "source": {
+    "extractorName": "csharp",
+    "id": "csharp/autobuilder/buildless/failed",
+    "name": "C# analysis with build-mode 'none' failed"
+  },
+  "visibility": {
+    "cliSummaryTable": true,
+    "statusPage": true,
+    "telemetry": true
+  }
+}
+{
+  "markdownMessage": "C# with build-mode set to 'none'. This means that all C# source in the working directory will be scanned, with build tools, such as Nuget and Dotnet CLIs, only contributing information about external dependencies.",
+  "severity": "note",
+  "source": {
+    "extractorName": "csharp",
+    "id": "csharp/autobuilder/buildless/mode-active",
+    "name": "C# with build-mode set to 'none'"
+  },
+  "visibility": {
+    "cliSummaryTable": true,
+    "statusPage": true,
+    "telemetry": true
+  }
+}
diff --git a/csharp/ql/integration-tests/all-platforms/standalone_failed/standalone.csproj b/csharp/ql/integration-tests/all-platforms/standalone_failed/standalone.csproj
new file mode 100644
index 00000000000..324eba5d4ef
--- /dev/null
+++ b/csharp/ql/integration-tests/all-platforms/standalone_failed/standalone.csproj
@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+ <Target Name="DeleteBinObjFolders" BeforeTargets="Clean">
+   <RemoveDir Directories=".\bin" />
+   <RemoveDir Directories=".\obj" />
+ </Target>
+</Project>
diff --git a/csharp/ql/integration-tests/all-platforms/standalone_failed/test.py b/csharp/ql/integration-tests/all-platforms/standalone_failed/test.py
new file mode 100644
index 00000000000..403e8efff23
--- /dev/null
+++ b/csharp/ql/integration-tests/all-platforms/standalone_failed/test.py
@@ -0,0 +1,6 @@
+from create_database_utils import *
+from diagnostics_test_utils import *
+
+run_codeql_database_create([], db=None, lang="csharp", extra_args=["--build-mode=none"], runFunction=runUnsuccessfully)
+
+check_diagnostics()