diff --git a/taichi/analysis/gen_offline_cache_key.cpp b/taichi/analysis/gen_offline_cache_key.cpp
index a121e25fe14d3..f14297399d845 100644
--- a/taichi/analysis/gen_offline_cache_key.cpp
+++ b/taichi/analysis/gen_offline_cache_key.cpp
@@ -55,6 +55,8 @@ class ASTSerializer : public IRVisitor, public ExpressionVisitor {
  public:
   ASTSerializer(Program *prog, std::ostream *os)
       : ExpressionVisitor(true), prog_(prog), os_(os) {
+    // TODO(PGZXB): Set allow_undefined_visitor as false. (blocked by
+    // constant-folding)
     this->allow_undefined_visitor = true;
   }
 
@@ -272,6 +274,12 @@ class ASTSerializer : public IRVisitor, public ExpressionVisitor {
     emit(expr->var);
   }
 
+  void visit(GetElementExpression *expr) override {
+    emit(ExprOpCode::GetElementExpression);
+    emit(expr->src);
+    emit(expr->index);
+  }
+
   void visit(Block *block) override {
     emit(StmtOpCode::EnterBlock);
     emit(static_cast<std::size_t>(block->statements.size()));
diff --git a/taichi/inc/expressions.inc.h b/taichi/inc/expressions.inc.h
index b311e6fb5a441..eaf498ea9598e 100644
--- a/taichi/inc/expressions.inc.h
+++ b/taichi/inc/expressions.inc.h
@@ -24,3 +24,4 @@ PER_EXPRESSION(MeshIndexConversionExpression)
 PER_EXPRESSION(ReferenceExpression)
 PER_EXPRESSION(TextureOpExpression)
 PER_EXPRESSION(TexturePtrExpression)
+PER_EXPRESSION(GetElementExpression)