diff --git a/lib/Differentiator/StmtClone.cpp b/lib/Differentiator/StmtClone.cpp
index 095d134c8..3fd85853a 100644
--- a/lib/Differentiator/StmtClone.cpp
+++ b/lib/Differentiator/StmtClone.cpp
@@ -448,7 +448,7 @@ bool ReferencesUpdater::VisitStmt(clang::Stmt* S) {
 }
 
 void ReferencesUpdater::updateType(QualType QT) {
-  if (auto* varArrType = dyn_cast<VariableArrayType>(QT)) {
+  if (const auto* varArrType = dyn_cast<VariableArrayType>(QT)) {
     TraverseStmt(varArrType->getSizeExpr());
   }
 }