diff --git a/src/services/services.ts b/src/services/services.ts
index 9cb7d6638b9..90f9acd82ea 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -1543,7 +1543,7 @@ namespace ts {
                 }
             }
             else {
-                sourceFiles = program.getSourceFiles();
+                sourceFiles = program.getSourceFiles().slice();
             }
 
             return FindAllReferences.findReferencedEntries(program, cancellationToken, sourceFiles, getValidSourceFile(fileName), position, options);