diff --git a/src/Compilers/Core/Portable/DiagnosticAnalyzer/AnalyzerDriver.cs b/src/Compilers/Core/Portable/DiagnosticAnalyzer/AnalyzerDriver.cs
index 89060a9af3a71326e088c1f1a15d5b37c9abd23c..8f2e44f97b13f080957237984bd05ac3d35d31b3 100644
--- a/src/Compilers/Core/Portable/DiagnosticAnalyzer/AnalyzerDriver.cs
+++ b/src/Compilers/Core/Portable/DiagnosticAnalyzer/AnalyzerDriver.cs
@@ -1853,6 +1853,11 @@ private static void ComputeDeclarationsInNode(SemanticModel semanticModel, ISymb
             // Mark completion if we successfully executed all actions and only if we are analyzing a span containing the entire syntax node.
             if (success && analysisStateOpt != null && !declarationAnalysisData.IsPartialAnalysis)
             {
+                // Ensure that we do not mark declaration complete/clear state if cancellation was requested.
+                // Other thread(s) might still be executing analysis, and clearing state could lead to corrupt execution
+                // or unknown exceptions.
+                cancellationToken.ThrowIfCancellationRequested();
+
                 foreach (var analyzer in analysisScope.Analyzers)
                 {
                     analysisStateOpt.MarkDeclarationComplete(symbol, declarationIndex, analyzer);