diff --git a/src/LanguageServer/Protocol/Features/Diagnostics/EngineV2/DiagnosticIncrementalAnalyzer_IncrementalAnalyzer.cs b/src/LanguageServer/Protocol/Features/Diagnostics/EngineV2/DiagnosticIncrementalAnalyzer_IncrementalAnalyzer.cs
index 99147ea7972d1..5cf2bfc87a966 100644
--- a/src/LanguageServer/Protocol/Features/Diagnostics/EngineV2/DiagnosticIncrementalAnalyzer_IncrementalAnalyzer.cs
+++ b/src/LanguageServer/Protocol/Features/Diagnostics/EngineV2/DiagnosticIncrementalAnalyzer_IncrementalAnalyzer.cs
@@ -38,8 +38,8 @@ public async Task<ImmutableArray<DiagnosticData>> ForceAnalyzeProjectAsync(Proje
                     // Try to add the new computed data to the CWT.  But use any existing value that another thread
                     // might have beaten us to storing in it.
 #if NET
-                    _projectToForceAnalysisData.TryAdd(project, box);
-                    Contract.ThrowIfFalse(_projectToForceAnalysisData.TryGetValue(project, out box));
+                    if (!_projectToForceAnalysisData.TryAdd(project, box))
+                        Contract.ThrowIfFalse(_projectToForceAnalysisData.TryGetValue(project, out box));
 #else
                     box = _projectToForceAnalysisData.GetValue(project, _ => box);
 #endif