diff --git a/base/src/test/user_model/test_defined_names.rs b/base/src/test/user_model/test_defined_names.rs
index 23c50dd..d1c7f58 100644
--- a/base/src/test/user_model/test_defined_names.rs
+++ b/base/src/test/user_model/test_defined_names.rs
@@ -396,3 +396,30 @@ fn undo_redo() {
         Ok("Hola!".to_string())
     );
 }
+
+#[test]
+fn change_scope_to_first_sheet() {
+    let mut model = UserModel::new_empty("model", "en", "UTC").unwrap();
+    model.new_sheet().unwrap();
+    model.set_user_input(0, 1, 1, "Hello").unwrap();
+    model
+        .set_user_input(1, 2, 1, r#"=CONCATENATE(MyName, " world!")"#)
+        .unwrap();
+    model
+        .new_defined_name("myName", None, "Sheet1!$A$1")
+        .unwrap();
+
+    assert_eq!(
+        model.get_formatted_cell_value(1, 2, 1),
+        Ok("Hello world!".to_string())
+    );
+
+    model
+        .update_defined_name("myName", None, "myName", Some(0), "Sheet1!$A$1")
+        .unwrap();
+
+    assert_eq!(
+        model.get_formatted_cell_value(1, 2, 1),
+        Ok("#NAME?".to_string())
+    );
+}
diff --git a/webapp/IronCalc/src/components/NameManagerDialog/NameManagerDialog.tsx b/webapp/IronCalc/src/components/NameManagerDialog/NameManagerDialog.tsx
index 0c735b4..baa5921 100644
--- a/webapp/IronCalc/src/components/NameManagerDialog/NameManagerDialog.tsx
+++ b/webapp/IronCalc/src/components/NameManagerDialog/NameManagerDialog.tsx
@@ -98,9 +98,10 @@ function NameManagerDialog(properties: NameManagerDialogProperties) {
         ) : (
           <NameListWrapper>
             {definedNameList.map((definedName, index) => {
-              const scopeName = definedName.scope
-                ? worksheets[definedName.scope].name
-                : "[global]";
+              const scopeName =
+                definedName.scope !== undefined
+                  ? worksheets[definedName.scope].name
+                  : "[global]";
               if (index === editingNameIndex) {
                 return (
                   <NamedRangeActive
@@ -117,7 +118,7 @@ function NameManagerDialog(properties: NameManagerDialogProperties) {
                       const scope_index = worksheets.findIndex(
                         (s) => s.name === newScope,
                       );
-                      const scope = scope_index > 0 ? scope_index : undefined;
+                      const scope = scope_index >= 0 ? scope_index : undefined;
                       try {
                         updateDefinedName(
                           definedName.name,