diff --git a/xls/jit/ir_builder_visitor.cc b/xls/jit/ir_builder_visitor.cc
index 5dad0c9a6f..0bd13540be 100644
--- a/xls/jit/ir_builder_visitor.cc
+++ b/xls/jit/ir_builder_visitor.cc
@@ -2238,6 +2238,7 @@ absl::Status IrBuilderVisitor::HandleInvoke(Invoke* invoke) {
 
   llvm::Value* output_buffer = node_context.GetOutputPtr(0);
   std::vector<llvm::Value*> operand_ptrs;
+  operand_ptrs.reserve(invoke->operand_count());
   for (int64_t i = 0; i < invoke->operand_count(); ++i) {
     operand_ptrs.push_back(node_context.GetOperandPtr(i));
   }
@@ -3043,6 +3044,7 @@ absl::Status IrBuilderVisitor::HandleNaryOp(
       NewNodeIrContext(node,
                        NumberedStrings("operand", node->operand_count())));
   std::vector<llvm::Value*> args;
+  args.reserve(node->operand_count());
   for (int64_t i = 0; i < node->operand_count(); ++i) {
     args.push_back(node_context.LoadOperand(i));
   }
diff --git a/xls/jit/type_layout.cc b/xls/jit/type_layout.cc
index 8b9082e703..3acf1dcf37 100644
--- a/xls/jit/type_layout.cc
+++ b/xls/jit/type_layout.cc
@@ -127,6 +127,7 @@ Value TypeLayout::NativeLayoutToValueInternal(Type* element_type,
   if (element_type->IsTuple()) {
     TupleType* tuple_type = element_type->AsTupleOrDie();
     std::vector<Value> elements;
+    elements.reserve(tuple_type->size());
     for (int64_t i = 0; i < tuple_type->size(); ++i) {
       elements.push_back(NativeLayoutToValueInternal(
           tuple_type->element_type(i), buffer, leaf_index));
@@ -137,6 +138,7 @@ Value TypeLayout::NativeLayoutToValueInternal(Type* element_type,
   CHECK(element_type->IsArray());
   ArrayType* array_type = element_type->AsArrayOrDie();
   std::vector<Value> elements;
+  elements.reserve(array_type->size());
   for (int64_t i = 0; i < array_type->size(); ++i) {
     elements.push_back(NativeLayoutToValueInternal(array_type->element_type(),
                                                    buffer, leaf_index));