diff --git a/testing/tests/test_annotations.rs b/testing/tests/test_annotations.rs
index ba77f8f9..b2971fea 100644
--- a/testing/tests/test_annotations.rs
+++ b/testing/tests/test_annotations.rs
@@ -25,7 +25,7 @@ trait SerializeWith: Sized {
 }
 
 trait DeserializeWith: Sized {
-    fn deserialize_with<D>(de: &mut D) -> Result<Self, D::Error>
+    fn deserialize_with<D>(de: D) -> Result<Self, D::Error>
         where D: Deserializer;
 }
 
@@ -50,7 +50,7 @@ impl SerializeWith for i32 {
 }
 
 impl DeserializeWith for i32 {
-    fn deserialize_with<D>(de: &mut D) -> Result<Self, D::Error>
+    fn deserialize_with<D>(de: D) -> Result<Self, D::Error>
         where D: Deserializer
     {
         if try!(Deserialize::deserialize(de)) {
@@ -239,7 +239,7 @@ impl Default for NotDeserializeStruct {
 }
 
 impl DeserializeWith for NotDeserializeStruct {
-    fn deserialize_with<D>(_: &mut D) -> Result<Self, D::Error>
+    fn deserialize_with<D>(_: D) -> Result<Self, D::Error>
         where D: Deserializer
     {
         panic!()
diff --git a/testing/tests/test_gen.rs b/testing/tests/test_gen.rs
index 24338312..3945a924 100644
--- a/testing/tests/test_gen.rs
+++ b/testing/tests/test_gen.rs
@@ -299,7 +299,7 @@ trait SerializeWith {
 }
 
 trait DeserializeWith: Sized {
-    fn deserialize_with<D: Deserializer>(_: &mut D) -> StdResult<Self, D::Error>;
+    fn deserialize_with<D: Deserializer>(_: D) -> StdResult<Self, D::Error>;
 }
 
 // Implements neither Serialize nor Deserialize
@@ -309,7 +309,7 @@ fn ser_x<S: Serializer>(_: &X, _: &mut S) -> StdResult<(), S::Error> {
     unimplemented!()
 }
 
-fn de_x<D: Deserializer>(_: &mut D) -> StdResult<X, D::Error> {
+fn de_x<D: Deserializer>(_: D) -> StdResult<X, D::Error> {
     unimplemented!()
 }
 
@@ -320,7 +320,7 @@ impl SerializeWith for X {
 }
 
 impl DeserializeWith for X {
-    fn deserialize_with<D: Deserializer>(_: &mut D) -> StdResult<Self, D::Error> {
+    fn deserialize_with<D: Deserializer>(_: D) -> StdResult<Self, D::Error> {
         unimplemented!()
     }
 }