diff --git a/Cargo.toml b/Cargo.toml
index c6b3ea4..fdcaa89 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -41,6 +41,10 @@ unstable = []
 name = "simple"
 path = "examples/simple.rs"
 
+[[example]]
+name = "form"
+path = "examples/form.rs"
+
 [[example]]
 name = "async"
 path = "examples/async.rs"
diff --git a/examples/form.rs b/examples/form.rs
new file mode 100644
index 0000000..41d1b82
--- /dev/null
+++ b/examples/form.rs
@@ -0,0 +1,9 @@
+extern crate reqwest;
+
+fn main() {
+    reqwest::Client::new()
+        .post("http://www.baidu.com")
+        .form(&[("one", "1")])
+        .send()
+        .unwrap();
+}
diff --git a/src/async_impl/request.rs b/src/async_impl/request.rs
index 0c2e359..eca5981 100644
--- a/src/async_impl/request.rs
+++ b/src/async_impl/request.rs
@@ -144,7 +144,7 @@ impl RequestBuilder {
     /// # Errors
     /// This method will fail if the object you provide cannot be serialized
     /// into a query string.
-    pub fn query<T: Serialize>(&mut self, query: &T) -> &mut RequestBuilder {
+    pub fn query<T: Serialize + ?Sized>(&mut self, query: &T) -> &mut RequestBuilder {
         if let Some(req) = request_mut(&mut self.request, &self.err) {
             let url = req.url_mut();
             let mut pairs = url.query_pairs_mut();
@@ -158,7 +158,7 @@ impl RequestBuilder {
     }
 
     /// Send a form body.
-    pub fn form<T: Serialize>(&mut self, form: &T) -> &mut RequestBuilder {
+    pub fn form<T: Serialize + ?Sized>(&mut self, form: &T) -> &mut RequestBuilder {
         if let Some(req) = request_mut(&mut self.request, &self.err) {
             match serde_urlencoded::to_string(form) {
                 Ok(body) => {
@@ -177,7 +177,7 @@ impl RequestBuilder {
     ///
     /// Serialization can fail if `T`'s implementation of `Serialize` decides to
     /// fail, or if `T` contains a map with non-string keys.
-    pub fn json<T: Serialize>(&mut self, json: &T) -> &mut RequestBuilder {
+    pub fn json<T: Serialize + ?Sized>(&mut self, json: &T) -> &mut RequestBuilder {
         if let Some(req) = request_mut(&mut self.request, &self.err) {
             match serde_json::to_vec(json) {
                 Ok(body) => {
diff --git a/src/request.rs b/src/request.rs
index 355a0fc..f1ad19e 100644
--- a/src/request.rs
+++ b/src/request.rs
@@ -240,7 +240,7 @@ impl RequestBuilder {
     /// # Errors
     /// This method will fail if the object you provide cannot be serialized
     /// into a query string.
-    pub fn query<T: Serialize>(&mut self, query: &T) -> &mut RequestBuilder {
+    pub fn query<T: Serialize + ?Sized>(&mut self, query: &T) -> &mut RequestBuilder {
         if let Some(req) = request_mut(&mut self.request, &self.err) {
             let url = req.url_mut();
             let mut pairs = url.query_pairs_mut();
@@ -279,7 +279,7 @@ impl RequestBuilder {
     ///
     /// This method fails if the passed value cannot be serialized into
     /// url encoded format
-    pub fn form<T: Serialize>(&mut self, form: &T) -> &mut RequestBuilder {
+    pub fn form<T: Serialize + ?Sized>(&mut self, form: &T) -> &mut RequestBuilder {
         if let Some(req) = request_mut(&mut self.request, &self.err) {
             match serde_urlencoded::to_string(form) {
                 Ok(body) => {
@@ -317,7 +317,7 @@ impl RequestBuilder {
     ///
     /// Serialization can fail if `T`'s implementation of `Serialize` decides to
     /// fail, or if `T` contains a map with non-string keys.
-    pub fn json<T: Serialize>(&mut self, json: &T) -> &mut RequestBuilder {
+    pub fn json<T: Serialize + ?Sized>(&mut self, json: &T) -> &mut RequestBuilder {
         if let Some(req) = request_mut(&mut self.request, &self.err) {
             match serde_json::to_vec(json) {
                 Ok(body) => {