diff --git a/src/value/ser.rs b/src/value/ser.rs
index e869ae160..b292f9820 100644
--- a/src/value/ser.rs
+++ b/src/value/ser.rs
@@ -505,6 +505,10 @@ impl serde::Serializer for MapKeySerializer {
         Ok(value.to_string())
     }
 
+    fn serialize_i128(self, value: i128) -> Result<String> {
+        Ok(value.to_string())
+    }
+
     fn serialize_u8(self, value: u8) -> Result<String> {
         Ok(value.to_string())
     }
@@ -521,6 +525,10 @@ impl serde::Serializer for MapKeySerializer {
         Ok(value.to_string())
     }
 
+    fn serialize_u128(self, value: u128) -> Result<String> {
+        Ok(value.to_string())
+    }
+
     fn serialize_f32(self, value: f32) -> Result<String> {
         if value.is_finite() {
             Ok(ryu::Buffer::new().format_finite(value).to_owned())