diff --git a/include/clad/Differentiator/VisitorBase.h b/include/clad/Differentiator/VisitorBase.h
index a07be18f7..9457232c1 100644
--- a/include/clad/Differentiator/VisitorBase.h
+++ b/include/clad/Differentiator/VisitorBase.h
@@ -408,7 +408,7 @@ namespace clad {
     /// a sequence of indices.
     clang::Expr*
     BuildArraySubscript(clang::Expr* Base,
-                        llvm::SmallVectorImpl<clang::Expr*>& IS);
+                        const llvm::SmallVectorImpl<clang::Expr*>& IS);
     /// Find namespace clad declaration.
     clang::NamespaceDecl* GetCladNamespace();
     /// Find declaration of clad::class templated type
diff --git a/lib/Differentiator/VisitorBase.cpp b/lib/Differentiator/VisitorBase.cpp
index 05e27dc10..3b1d2fea8 100644
--- a/lib/Differentiator/VisitorBase.cpp
+++ b/lib/Differentiator/VisitorBase.cpp
@@ -418,19 +418,21 @@ namespace clad {
   }
 
   Expr* VisitorBase::BuildArraySubscript(
-      Expr* Base, llvm::SmallVectorImpl<clang::Expr*>& Indices) {
+      Expr* Base, const llvm::SmallVectorImpl<clang::Expr*>& Indices) {
     Expr* result = Base;
     SourceLocation fakeLoc = utils::GetValidSLoc(m_Sema);
-    if (utils::isArrayOrPointerType(Base->getType()))
+    if (utils::isArrayOrPointerType(Base->getType())) {
       for (Expr* I : Indices)
         result =
             m_Sema.CreateBuiltinArraySubscriptExpr(result, fakeLoc, I, fakeLoc)
                 .get();
-    else
+    } else {
+      Expr* idx = Indices.back();
       result = m_Sema
-                   .ActOnArraySubscriptExpr(getCurrentScope(), Base, fakeLoc,
-                                            Indices.back(), fakeLoc)
+                   .ActOnArraySubscriptExpr(getCurrentScope(), Base, fakeLoc, idx,
+                                            fakeLoc)
                    .get();
+    }
     return result;
   }