diff --git a/src/VisualStudio/Core/Impl/SolutionExplorer/SymbolTree/RootSymbolTreeItemSourceProvider.cs b/src/VisualStudio/Core/Impl/SolutionExplorer/SymbolTree/RootSymbolTreeItemSourceProvider.cs
index 2e4bb424200fc..972bab8d8b786 100644
--- a/src/VisualStudio/Core/Impl/SolutionExplorer/SymbolTree/RootSymbolTreeItemSourceProvider.cs
+++ b/src/VisualStudio/Core/Impl/SolutionExplorer/SymbolTree/RootSymbolTreeItemSourceProvider.cs
@@ -116,7 +116,10 @@ private async ValueTask UpdateCollectionSourcesAsync(
         lock (_filePathToCollectionSources)
         {
             foreach (var filePath in updatedFilePaths)
-                sources.AddRange(_filePathToCollectionSources[filePath]);
+            {
+                if (_filePathToCollectionSources.TryGetValue(filePath, out var pathSources))
+                    sources.AddRange(pathSources);
+            }
         }
 
         // Update all the affected documents in parallel.