diff --git a/src/ext/json.rs b/src/ext/json.rs
index e7caaf2..ba3a054 100644
--- a/src/ext/json.rs
+++ b/src/ext/json.rs
@@ -10,12 +10,6 @@ impl ToJson for &str {
     }
 }
 
-impl ToJson for &String {
-    fn to_json(&self) -> Option<JsonValue> {
-        Some(JsonValue::String((*self).to_string()))
-    }
-}
-
 impl ToJson for String {
     fn to_json(&self) -> Option<JsonValue> {
         Some(JsonValue::String(self.to_string()))
@@ -28,9 +22,9 @@ impl ToJson for JsonValue {
     }
 }
 
-impl ToJson for &JsonValue {
+impl<T: ToJson> ToJson for &T {
     fn to_json(&self) -> Option<JsonValue> {
-        Some((*self).clone())
+        (*self).to_json()
     }
 }
 
diff --git a/src/pixiv_link.rs b/src/pixiv_link.rs
index 7f706ce..70c9424 100644
--- a/src/pixiv_link.rs
+++ b/src/pixiv_link.rs
@@ -58,9 +58,9 @@ impl ToJson for PixivID {
     }
 }
 
-impl ToPixivID for &PixivID {
+impl ToPixivID for PixivID {
     fn to_pixiv_id(&self) -> Option<PixivID> {
-        Some((*self).clone())
+        Some(self.clone())
     }
 }
 
@@ -82,6 +82,12 @@ impl ToPixivID for u64 {
     }
 }
 
+impl<T: ToPixivID> ToPixivID for &T {
+    fn to_pixiv_id(&self) -> Option<PixivID> {
+        (*self).to_pixiv_id()
+    }
+}
+
 impl TryInto<u64> for PixivID {
     type Error = ();
     fn try_into(self) -> Result<u64, Self::Error> {