diff --git a/src/PowerShellEditorServices/Services/Analysis/AnalysisService.cs b/src/PowerShellEditorServices/Services/Analysis/AnalysisService.cs
index ef7979e55..6b2d25d27 100644
--- a/src/PowerShellEditorServices/Services/Analysis/AnalysisService.cs
+++ b/src/PowerShellEditorServices/Services/Analysis/AnalysisService.cs
@@ -410,7 +410,7 @@ private async Task DelayThenInvokeDiagnosticsAsync(ScriptFile[] filesToAnalyze,
 
         private void PublishScriptDiagnostics(ScriptFile scriptFile, IReadOnlyList<ScriptFileMarker> markers)
         {
-            var diagnostics = new Diagnostic[scriptFile.DiagnosticMarkers.Count];
+            var diagnostics = new Diagnostic[markers.Count];
 
             CorrectionTableEntry fileCorrections = _mostRecentCorrectionsByFile.GetOrAdd(
                 scriptFile,
diff --git a/src/PowerShellEditorServices/Services/TextDocument/Handlers/ReferencesHandler.cs b/src/PowerShellEditorServices/Services/TextDocument/Handlers/ReferencesHandler.cs
index 9917c557f..81dc17f8c 100644
--- a/src/PowerShellEditorServices/Services/TextDocument/Handlers/ReferencesHandler.cs
+++ b/src/PowerShellEditorServices/Services/TextDocument/Handlers/ReferencesHandler.cs
@@ -39,7 +39,7 @@ public TextDocumentRegistrationOptions GetRegistrationOptions()
             };
         }
 
-        public async Task<LocationContainer> Handle(ReferenceParams request, CancellationToken cancellationToken)
+        public Task<LocationContainer> Handle(ReferenceParams request, CancellationToken cancellationToken)
         {
             ScriptFile scriptFile = _workspaceService.GetFile(request.TextDocument.Uri);
 
@@ -69,7 +69,7 @@ public async Task<LocationContainer> Handle(ReferenceParams request, Cancellatio
                 }
             }
 
-            return new LocationContainer(locations);
+            return Task.FromResult(new LocationContainer(locations));
         }
 
         public void SetCapability(ReferencesCapability capability)
diff --git a/src/PowerShellEditorServices/Services/TextDocument/Handlers/TextDocumentHandler.cs b/src/PowerShellEditorServices/Services/TextDocument/Handlers/TextDocumentHandler.cs
index 784593d83..73c779cac 100644
--- a/src/PowerShellEditorServices/Services/TextDocument/Handlers/TextDocumentHandler.cs
+++ b/src/PowerShellEditorServices/Services/TextDocument/Handlers/TextDocumentHandler.cs
@@ -21,6 +21,7 @@ namespace Microsoft.PowerShell.EditorServices.Handlers
 {
     class TextDocumentHandler : ITextDocumentSyncHandler
     {
+        private static readonly Uri s_fakeUri = new Uri("Untitled:fake");
 
         private readonly ILogger _logger;
         private readonly AnalysisService _analysisService;
@@ -82,9 +83,16 @@ public Task<Unit> Handle(DidOpenTextDocumentParams notification, CancellationTok
                     notification.TextDocument.Uri,
                     notification.TextDocument.Text);
 
-            // Kick off script diagnostics without blocking the response
-            // TODO: Get all recently edited files in the workspace
-            _analysisService.RunScriptDiagnostics(new ScriptFile[] { openedFile }, token);
+            if (LspUtils.PowerShellDocumentSelector.IsMatch(new TextDocumentAttributes(
+                // We use a fake Uri because we only want to test the LanguageId here and not if the
+                // file ends in ps*1.
+                s_fakeUri,
+                notification.TextDocument.LanguageId)))
+            {
+                // Kick off script diagnostics if we got a PowerShell file without blocking the response
+                // TODO: Get all recently edited files in the workspace
+                _analysisService.RunScriptDiagnostics(new ScriptFile[] { openedFile }, token);
+            }
 
             _logger.LogTrace("Finished opening document.");
             return Unit.Task;
diff --git a/test/PowerShellEditorServices.Test.E2E/LanguageServerProtocolMessageTests.cs b/test/PowerShellEditorServices.Test.E2E/LanguageServerProtocolMessageTests.cs
index 8e1501814..5582cd68b 100644
--- a/test/PowerShellEditorServices.Test.E2E/LanguageServerProtocolMessageTests.cs
+++ b/test/PowerShellEditorServices.Test.E2E/LanguageServerProtocolMessageTests.cs
@@ -59,7 +59,7 @@ public void Dispose()
             Diagnostics.Clear();
         }
 
-        private string NewTestFile(string script, bool isPester = false)
+        private string NewTestFile(string script, bool isPester = false, string languageId = "powershell")
         {
             string fileExt = isPester ? ".Tests.ps1" : ".ps1";
             string filePath = Path.Combine(s_binDir, Path.GetRandomFileName() + fileExt);
@@ -69,7 +69,7 @@ private string NewTestFile(string script, bool isPester = false)
             {
                 TextDocument = new TextDocumentItem
                 {
-                    LanguageId = "powershell",
+                    LanguageId = languageId,
                     Version = 0,
                     Text = script,
                     Uri = new Uri(filePath)
@@ -145,6 +145,15 @@ public async Task CanReceiveDiagnosticsFromFileOpen()
             Assert.Equal("PSUseDeclaredVarsMoreThanAssignments", diagnostic.Code);
         }
 
+        [Fact]
+        public async Task WontReceiveDiagnosticsFromFileOpenThatIsNotPowerShell()
+        {
+            NewTestFile("$a = 4", languageId: "plaintext");
+            await Task.Delay(2000);
+
+            Assert.Empty(Diagnostics);
+        }
+
         [Fact]
         public async Task CanReceiveDiagnosticsFromFileChanged()
         {