diff --git a/csharp/autobuilder/Semmle.Autobuild.CSharp/DotNetRule.cs b/csharp/autobuilder/Semmle.Autobuild.CSharp/DotNetRule.cs
index 43efcd0352f0..7224a8ff76b9 100644
--- a/csharp/autobuilder/Semmle.Autobuild.CSharp/DotNetRule.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.CSharp/DotNetRule.cs
@@ -32,7 +32,7 @@ public BuildScript Analyse(IAutobuilder<CSharpAutobuildOptions> builder, bool au
                 NotDotNetProjects = builder.ProjectsOrSolutionsToBuild
                     .SelectMany(p => new[] { p }.Concat(p.IncludedProjects))
                     .OfType<Project<CSharpAutobuildOptions>>()
-                    .Where(p => !p.DotNetProject);
+                    .Where(p => !p.MaybeDotNetProject);
                 var notDotNetProject = NotDotNetProjects.FirstOrDefault();
 
                 if (notDotNetProject is not null)
diff --git a/csharp/autobuilder/Semmle.Autobuild.Shared/Project.cs b/csharp/autobuilder/Semmle.Autobuild.Shared/Project.cs
index c318ef09805d..0e95070ab357 100644
--- a/csharp/autobuilder/Semmle.Autobuild.Shared/Project.cs
+++ b/csharp/autobuilder/Semmle.Autobuild.Shared/Project.cs
@@ -17,7 +17,7 @@ public class Project<TAutobuildOptions> : ProjectOrSolution<TAutobuildOptions> w
         /// <summary>
         /// Holds if this project is for .Net core.
         /// </summary>
-        public bool DotNetProject { get; private set; }
+        public bool MaybeDotNetProject { get; init; }
 
         public bool ValidToolsVersion { get; private set; }
 
@@ -32,7 +32,11 @@ public Project(Autobuilder<TAutobuildOptions> builder, string path) : base(build
             includedProjectsLazy = new Lazy<List<Project<TAutobuildOptions>>>(() => new List<Project<TAutobuildOptions>>());
 
             if (!builder.Actions.FileExists(FullPath))
+            {
+                // We can't out-rule that this is a dotnet project.
+                MaybeDotNetProject = true;
                 return;
+            }
 
             XmlDocument projFile;
             try
@@ -51,7 +55,7 @@ public Project(Autobuilder<TAutobuildOptions> builder, string path) : base(build
             {
                 if (root.HasAttribute("Sdk"))
                 {
-                    DotNetProject = true;
+                    MaybeDotNetProject = true;
                     return;
                 }