diff --git a/include/ftxui/screen/box.hpp b/include/ftxui/screen/box.hpp
index 9fc2792..3770803 100644
--- a/include/ftxui/screen/box.hpp
+++ b/include/ftxui/screen/box.hpp
@@ -15,7 +15,7 @@ struct Box {
   static auto Intersection(Box a, Box b) -> Box;
   static auto Union(Box a, Box b) -> Box;
   bool Contain(int x, int y) const;
-  bool IsEmpty();
+  bool IsEmpty() const;
   bool operator==(const Box& other) const;
   bool operator!=(const Box& other) const;
 };
diff --git a/src/ftxui/component/dropdown.cpp b/src/ftxui/component/dropdown.cpp
index 5f96580..e105852 100644
--- a/src/ftxui/component/dropdown.cpp
+++ b/src/ftxui/component/dropdown.cpp
@@ -32,7 +32,7 @@ Component Dropdown(ConstStringListRef entries, int* selected) {
 Component Dropdown(DropdownOption option) {
   class Impl : public ComponentBase, public DropdownOption {
    public:
-    Impl(DropdownOption option) : DropdownOption(std::move(option)) {
+    explicit Impl(DropdownOption option) : DropdownOption(std::move(option)) {
       FillDefault();
       checkbox_ = Checkbox(checkbox);
       radiobox_ = Radiobox(radiobox);
@@ -71,8 +71,8 @@ Component Dropdown(DropdownOption option) {
     }
 
     void FillDefault() {
-      open_ = std::move(checkbox.checked);
-      selected_ = std::move(radiobox.selected);
+      open_ = checkbox.checked;
+      selected_ = radiobox.selected;
       checkbox.checked = &*open_;
       radiobox.selected = &*selected_;
 
diff --git a/src/ftxui/screen/box.cpp b/src/ftxui/screen/box.cpp
index 0210153..e190305 100644
--- a/src/ftxui/screen/box.cpp
+++ b/src/ftxui/screen/box.cpp
@@ -41,7 +41,7 @@ bool Box::Contain(int x, int y) const {
 
 /// @return whether the box is empty.
 /// @ingroup screen
-bool Box::IsEmpty() {
+bool Box::IsEmpty() const {
   return x_min > x_max || y_min > y_max;
 }