diff --git a/src/Workspaces/Core/Portable/SymbolKey/SymbolKey.SymbolKeyWriter.cs b/src/Workspaces/Core/Portable/SymbolKey/SymbolKey.SymbolKeyWriter.cs
index 9afd8efdb3bad18090929051a1c26c055043eb2e..1419fef78bed0ffc116337765aa4ecb12271e320 100644
--- a/src/Workspaces/Core/Portable/SymbolKey/SymbolKey.SymbolKeyWriter.cs
+++ b/src/Workspaces/Core/Portable/SymbolKey/SymbolKey.SymbolKeyWriter.cs
@@ -244,7 +244,7 @@ internal void WriteLocation(Location location)
             {
                 location = location ?? Location.None;
 
-                WriteString(location.SourceTree.FilePath ?? "");
+                WriteString(location.SourceTree?.FilePath ?? "");
                 WriteInteger(location.SourceSpan.Start);
                 WriteInteger(location.SourceSpan.Length);
             }