diff --git a/langs/zh_TW_extra_key.json b/langs/zh_TW_extra_key.json
new file mode 100644
index 0000000..f73b892
--- /dev/null
+++ b/langs/zh_TW_extra_key.json
@@ -0,0 +1,4 @@
+{
+  "hello": "哈囉，世界！",
+  "goodbye": "再見"
+}
\ No newline at end of file
diff --git a/src/key_copy/json_gettext.rs b/src/key_copy/json_gettext.rs
index 3d14d25..56683d7 100644
--- a/src/key_copy/json_gettext.rs
+++ b/src/key_copy/json_gettext.rs
@@ -23,6 +23,7 @@ impl<'a> JSONGetText<'a> {
     /// Create a new JSONGetText instance with context and a default key.
     pub(crate) fn from_context_with_default_key(
         default_key: Key,
+        ignore_extra_keys: bool,
         mut context: Context<'a>,
     ) -> Result<JSONGetText<'a>, JSONGetTextBuildError> {
         if !context.contains_key(&default_key) {
@@ -36,12 +37,17 @@ impl<'a> JSONGetText<'a> {
         {
             for (key, mut map) in context {
                 {
-                    for map_key in map.keys() {
-                        if !default_map.contains_key(map_key) {
-                            return Err(JSONGetTextBuildError::TextInKeyNotInDefaultKey {
-                                key,
-                                text: map_key.clone(),
-                            });
+                    if ignore_extra_keys {
+                        map =
+                            map.into_iter().filter(|(k, _)| default_map.contains_key(k)).collect();
+                    } else {
+                        for map_key in map.keys() {
+                            if !default_map.contains_key(map_key) {
+                                return Err(JSONGetTextBuildError::TextInKeyNotInDefaultKey {
+                                    key,
+                                    text: map_key.clone(),
+                                });
+                            }
                         }
                     }
                 }
diff --git a/src/key_string/json_get_text_builder.rs b/src/key_string/json_get_text_builder.rs
index 421f2d6..19bf809 100644
--- a/src/key_string/json_get_text_builder.rs
+++ b/src/key_string/json_get_text_builder.rs
@@ -142,8 +142,12 @@ impl<'a> JSONGetTextBuilder<'a> {
     }
 
     /// Build a `JSONGetText` instance.
-    pub fn build(self) -> Result<JSONGetText<'a>, JSONGetTextBuildError> {
-        JSONGetText::from_context_with_default_key(self.default_key, self.context)
+    pub fn build(self, ignore_extra_keys: bool) -> Result<JSONGetText<'a>, JSONGetTextBuildError> {
+        JSONGetText::from_context_with_default_key(
+            self.default_key,
+            ignore_extra_keys,
+            self.context,
+        )
     }
 }
 
diff --git a/src/key_string/json_gettext.rs b/src/key_string/json_gettext.rs
index 41f7d61..b4ca087 100644
--- a/src/key_string/json_gettext.rs
+++ b/src/key_string/json_gettext.rs
@@ -23,6 +23,7 @@ impl<'a> JSONGetText<'a> {
     /// Create a new JSONGetText instance with context and a default key.
     pub(crate) fn from_context_with_default_key<S: AsRef<str> + Into<String>>(
         default_key: S,
+        ignore_extra_keys: bool,
         mut context: Context<'a>,
     ) -> Result<JSONGetText<'a>, JSONGetTextBuildError> {
         if !context.contains_key(default_key.as_ref()) {
@@ -38,25 +39,33 @@ impl<'a> JSONGetText<'a> {
         {
             for (key, mut map) in context {
                 {
-                    for map_key in map.keys() {
-                        if !default_map.contains_key(map_key) {
-                            return Err(JSONGetTextBuildError::TextInKeyNotInDefaultKey {
-                                key,
-                                text: map_key.clone(),
-                            });
+                    if ignore_extra_keys {
+                        map =
+                            map.into_iter().filter(|(k, _)| default_map.contains_key(k)).collect();
+                    } else {
+                        for map_key in map.keys() {
+                            if !default_map.contains_key(map_key) {
+                                return Err(JSONGetTextBuildError::TextInKeyNotInDefaultKey {
+                                    key,
+                                    text: map_key.clone(),
+                                });
+                            }
                         }
                     }
-                }
 
-                {
-                    for map_key in default_map.keys() {
-                        if !map.contains_key(map_key) {
-                            map.insert(map_key.clone(), default_map.get(map_key).unwrap().clone());
+                    {
+                        for map_key in default_map.keys() {
+                            if !map.contains_key(map_key) {
+                                map.insert(
+                                    map_key.clone(),
+                                    default_map.get(map_key).unwrap().clone(),
+                                );
+                            }
                         }
                     }
-                }
 
-                inner_context.insert(key, map);
+                    inner_context.insert(key, map);
+                }
             }
 
             inner_context.insert(default_key.clone().into(), default_map);
diff --git a/src/macros/mod.rs b/src/macros/mod.rs
index 8a8a674..b39550c 100644
--- a/src/macros/mod.rs
+++ b/src/macros/mod.rs
@@ -29,7 +29,7 @@ macro_rules! static_json_gettext_build {
                 builder.add_json($key, include_str!($crate::manifest_dir_macros::path!($path))).unwrap();
             )*
 
-            builder.build()
+            builder.build(false)
         }
     };
 }
diff --git a/tests/key_string_single.rs b/tests/key_string_single.rs
index fbae6a7..e73f238 100644
--- a/tests/key_string_single.rs
+++ b/tests/key_string_single.rs
@@ -3,6 +3,8 @@
 #[macro_use]
 extern crate json_gettext;
 
+use json_gettext::JSONGetTextBuilder;
+
 #[test]
 fn single_get() {
     let ctx = static_json_gettext_build!(
@@ -44,3 +46,15 @@ fn map_get() {
     assert_eq!("哈囉，世界！", map.get("hello").unwrap());
     assert_eq!("Rust!", map.get("rust").unwrap());
 }
+
+#[test]
+fn extra_keys() {
+    let mut builder = JSONGetTextBuilder::new("en_US");
+    builder.add_json_file("en_US", "langs/en_US.json").unwrap();
+    builder.add_json_file("zh_TW", "langs/zh_TW_extra_key.json").unwrap();
+    let ctx = builder.build(true).unwrap();
+
+    let map = ctx.get("zh_TW");
+    assert_eq!("哈囉，世界！", map.get("hello").unwrap());
+    assert_eq!(None, map.get("goodbye"));
+}