diff --git a/src/urlencoded/ser.rs b/src/urlencoded/ser.rs
index 874c6b08..9e6c5846 100644
--- a/src/urlencoded/ser.rs
+++ b/src/urlencoded/ser.rs
@@ -465,8 +465,8 @@ where
         value: &V,
     ) -> Result<(), Error> {
         let key_sink = key::KeySink::new(|key| {
-            let value_sink = value::ValueSink::new(self.urlencoder, &key);
-            value.serialize(part::PartSerializer::new(value_sink))?;
+            let mut value_sink = value::ValueSink::new(self.urlencoder, &key);
+            value.serialize(part::PartSerializer::new(&mut value_sink))?;
             self.key = None;
             Ok(())
         });
@@ -490,8 +490,8 @@ where
     ) -> Result<(), Error> {
         {
             let key = self.key.as_ref().ok_or_else(Error::no_key)?;
-            let value_sink = value::ValueSink::new(self.urlencoder, &key);
-            value.serialize(part::PartSerializer::new(value_sink))?;
+            let mut value_sink = value::ValueSink::new(self.urlencoder, &key);
+            value.serialize(part::PartSerializer::new(&mut value_sink))?;
         }
         self.key = None;
         Ok(())
@@ -515,8 +515,8 @@ where
         key: &'static str,
         value: &T,
     ) -> Result<(), Error> {
-        let value_sink = value::ValueSink::new(self.urlencoder, key);
-        value.serialize(part::PartSerializer::new(value_sink))
+        let mut value_sink = value::ValueSink::new(self.urlencoder, key);
+        value.serialize(part::PartSerializer::new(&mut value_sink))
     }
 
     fn end(self) -> Result<Self::Ok, Error> {
diff --git a/src/urlencoded/ser/pair.rs b/src/urlencoded/ser/pair.rs
index 5e991968..c12c404e 100644
--- a/src/urlencoded/ser/pair.rs
+++ b/src/urlencoded/ser/pair.rs
@@ -225,8 +225,8 @@ where
             }
             PairState::WaitingForValue { key } => {
                 let result = {
-                    let value_sink = ValueSink::new(self.urlencoder, &key);
-                    let value_serializer = PartSerializer::new(value_sink);
+                    let mut value_sink = ValueSink::new(self.urlencoder, &key);
+                    let value_serializer = PartSerializer::new(&mut value_sink);
                     value.serialize(value_serializer)
                 };
                 if result.is_ok() {
diff --git a/src/urlencoded/ser/value.rs b/src/urlencoded/ser/value.rs
index 37aa3b11..344a4280 100644
--- a/src/urlencoded/ser/value.rs
+++ b/src/urlencoded/ser/value.rs
@@ -30,8 +30,8 @@ where
     }
 }
 
-impl<'input, 'key, 'target, Target> Sink
-    for ValueSink<'input, 'key, 'target, Target>
+impl<'a, 'input, 'key, 'target, Target> Sink
+    for &'a mut ValueSink<'input, 'key, 'target, Target>
 where
     Target: 'target + UrlEncodedTarget,
 {