diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DotNet.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DotNet.cs
index 9d3d79e4c4ff..61df4e4ad48c 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DotNet.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DotNet.cs
@@ -66,6 +66,7 @@ private void Info()
         private string GetRestoreArgs(RestoreSettings restoreSettings)
         {
             var args = $"restore --no-dependencies \"{restoreSettings.File}\" --packages \"{restoreSettings.PackageDirectory}\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal";
+            args += " /p:RestoreIgnoreFailedSources=true";
 
             if (restoreSettings.ForceDotnetRefAssemblyFetching)
             {
diff --git a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/IDotNet.cs b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/IDotNet.cs
index eec6a2b8d3b2..3a1d1cc98094 100644
--- a/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/IDotNet.cs
+++ b/csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/IDotNet.cs
@@ -27,7 +27,8 @@ public partial record class RestoreResult(bool Success, IList<string> Output)
         private readonly Lazy<IEnumerable<string>> restoredProjects = new(() => GetFirstGroupOnMatch(RestoredProjectRegex(), Output));
         public IEnumerable<string> RestoredProjects => Success ? restoredProjects.Value : Array.Empty<string>();
 
-        private readonly Lazy<bool> hasNugetPackageSourceError = new(() => Output.Any(s => s.Contains("NU1301")));
+        // NU1301 is the error and NU1801 is the equivalent warning.
+        private readonly Lazy<bool> hasNugetPackageSourceError = new(() => Output.Any(s => s.Contains("NU1301") || s.Contains("NU1801")));
         public bool HasNugetPackageSourceError => hasNugetPackageSourceError.Value;
 
         private readonly Lazy<bool> hasNugetNoStablePackageVersionError = new(() => Output.Any(s => s.Contains("NU1103")));
diff --git a/csharp/extractor/Semmle.Extraction.Tests/DotNet.cs b/csharp/extractor/Semmle.Extraction.Tests/DotNet.cs
index a2996497e005..e4acfe14aeee 100644
--- a/csharp/extractor/Semmle.Extraction.Tests/DotNet.cs
+++ b/csharp/extractor/Semmle.Extraction.Tests/DotNet.cs
@@ -119,7 +119,7 @@ public void TestDotnetRestoreProjectToDirectory1()
 
             // Verify
             var lastArgs = dotnetCliInvoker.GetLastArgs();
-            Assert.Equal("restore --no-dependencies \"myproject.csproj\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal", lastArgs);
+            Assert.Equal("restore --no-dependencies \"myproject.csproj\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:RestoreIgnoreFailedSources=true", lastArgs);
         }
 
         [Fact]
@@ -134,7 +134,7 @@ public void TestDotnetRestoreProjectToDirectory2()
 
             // Verify
             var lastArgs = dotnetCliInvoker.GetLastArgs();
-            Assert.Equal("restore --no-dependencies \"myproject.csproj\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal --configfile \"myconfig.config\"", lastArgs);
+            Assert.Equal("restore --no-dependencies \"myproject.csproj\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:RestoreIgnoreFailedSources=true --configfile \"myconfig.config\"", lastArgs);
             Assert.Equal(2, res.AssetsFilePaths.Count());
             Assert.Contains("/path/to/project.assets.json", res.AssetsFilePaths);
             Assert.Contains("/path/to/project2.assets.json", res.AssetsFilePaths);
@@ -152,7 +152,7 @@ public void TestDotnetRestoreProjectToDirectory3()
 
             // Verify
             var lastArgs = dotnetCliInvoker.GetLastArgs();
-            Assert.Equal("restore --no-dependencies \"myproject.csproj\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal --configfile \"myconfig.config\" --force", lastArgs);
+            Assert.Equal("restore --no-dependencies \"myproject.csproj\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:RestoreIgnoreFailedSources=true --configfile \"myconfig.config\" --force", lastArgs);
             Assert.Equal(2, res.AssetsFilePaths.Count());
             Assert.Contains("/path/to/project.assets.json", res.AssetsFilePaths);
             Assert.Contains("/path/to/project2.assets.json", res.AssetsFilePaths);
@@ -170,7 +170,7 @@ public void TestDotnetRestoreSolutionToDirectory1()
 
             // Verify
             var lastArgs = dotnetCliInvoker.GetLastArgs();
-            Assert.Equal("restore --no-dependencies \"mysolution.sln\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal", lastArgs);
+            Assert.Equal("restore --no-dependencies \"mysolution.sln\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:RestoreIgnoreFailedSources=true", lastArgs);
             Assert.Equal(2, res.RestoredProjects.Count());
             Assert.Contains("/path/to/project.csproj", res.RestoredProjects);
             Assert.Contains("/path/to/project2.csproj", res.RestoredProjects);
@@ -192,7 +192,7 @@ public void TestDotnetRestoreSolutionToDirectory2()
 
             // Verify
             var lastArgs = dotnetCliInvoker.GetLastArgs();
-            Assert.Equal("restore --no-dependencies \"mysolution.sln\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal", lastArgs);
+            Assert.Equal("restore --no-dependencies \"mysolution.sln\" --packages \"mypackages\" /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:RestoreIgnoreFailedSources=true", lastArgs);
             Assert.Empty(res.RestoredProjects);
             Assert.Empty(res.AssetsFilePaths);
         }