diff --git a/serde/Cargo.toml b/serde/Cargo.toml
index 1e741936..30b89fbc 100644
--- a/serde/Cargo.toml
+++ b/serde/Cargo.toml
@@ -18,7 +18,7 @@ std = []
 unstable = []
 alloc = ["unstable"]
 collections = ["alloc"]
-unstable-testing = ["unstable", "std"]
+unstable-testing = ["clippy", "unstable", "std"]
 
 [dependencies]
 clippy = { version = "^0.*", optional = true }
diff --git a/serde/src/de/value.rs b/serde/src/de/value.rs
index f8e98bf8..9a74f9e0 100644
--- a/serde/src/de/value.rs
+++ b/serde/src/de/value.rs
@@ -128,7 +128,7 @@ impl fmt::Display for Error {
                 write!(formatter, "Unknown variant: {}", variant)
             }
             Error::UnknownField(ref field) => write!(formatter, "Unknown field: {}", field),
-            Error::MissingField(ref field) => write!(formatter, "Missing field: {}", field),
+            Error::MissingField(field) => write!(formatter, "Missing field: {}", field),
         }
     }
 }
diff --git a/serde_codegen/Cargo.toml b/serde_codegen/Cargo.toml
index f5b20603..1395ca4f 100644
--- a/serde_codegen/Cargo.toml
+++ b/serde_codegen/Cargo.toml
@@ -14,7 +14,7 @@ include = ["Cargo.toml", "build.rs", "src/**/*.rs", "src/lib.rs.in"]
 [features]
 default = ["with-syntex"]
 unstable = ["quasi_macros"]
-unstable-testing = []
+unstable-testing = ["clippy"]
 with-syntex = [
     "quasi/with-syntex",
     "quasi_codegen",
diff --git a/serde_codegen_internals/Cargo.toml b/serde_codegen_internals/Cargo.toml
index 3181eb19..62b24f2e 100644
--- a/serde_codegen_internals/Cargo.toml
+++ b/serde_codegen_internals/Cargo.toml
@@ -12,7 +12,7 @@ include = ["Cargo.toml", "src/**/*.rs"]
 
 [features]
 default = ["with-syntex"]
-unstable-testing = []
+unstable-testing = ["clippy"]
 with-syntex = ["syntex_syntax", "syntex_errors"]
 
 [dependencies]
diff --git a/serde_codegen_internals/src/attr.rs b/serde_codegen_internals/src/attr.rs
index 0b2ebf72..8d8d595b 100644
--- a/serde_codegen_internals/src/attr.rs
+++ b/serde_codegen_internals/src/attr.rs
@@ -449,12 +449,14 @@ impl Field {
     }
 }
 
+type SerAndDe<T> = (Option<Spanned<T>>, Option<Spanned<T>>);
+
 fn get_ser_and_de<T, F>(
     cx: &ExtCtxt,
     attribute: &'static str,
     items: &[P<ast::MetaItem>],
     f: F
-) -> Result<(Option<Spanned<T>>, Option<Spanned<T>>), ()>
+) -> Result<SerAndDe<T>, ()>
     where F: Fn(&ExtCtxt, &str, &ast::Lit) -> Result<T, ()>,
 {
     let mut ser_item = Attr::none(cx, attribute);
@@ -492,21 +494,21 @@ fn get_ser_and_de<T, F>(
 fn get_renames(
     cx: &ExtCtxt,
     items: &[P<ast::MetaItem>],
-) -> Result<(Option<Spanned<InternedString>>, Option<Spanned<InternedString>>), ()> {
+) -> Result<SerAndDe<InternedString>, ()> {
     get_ser_and_de(cx, "rename", items, get_str_from_lit)
 }
 
 fn get_where_predicates(
     cx: &ExtCtxt,
     items: &[P<ast::MetaItem>],
-) -> Result<(Option<Spanned<Vec<ast::WherePredicate>>>, Option<Spanned<Vec<ast::WherePredicate>>>), ()> {
+) -> Result<SerAndDe<Vec<ast::WherePredicate>>, ()> {
     get_ser_and_de(cx, "bound", items, parse_lit_into_where)
 }
 
 pub fn get_serde_meta_items(attr: &ast::Attribute) -> Option<&[P<ast::MetaItem>]> {
     match attr.node.value.node {
         ast::MetaItemKind::List(ref name, ref items) if name == &"serde" => {
-            attr::mark_used(&attr);
+            attr::mark_used(attr);
             Some(items)
         }
         _ => None
@@ -570,7 +572,7 @@ fn get_str_from_lit(cx: &ExtCtxt, name: &str, lit: &ast::Lit) -> Result<Interned
                          name,
                          lit_to_string(lit)));
 
-            return Err(());
+            Err(())
         }
     }
 }
diff --git a/serde_macros/Cargo.toml b/serde_macros/Cargo.toml
index 4f41e676..07e85110 100644
--- a/serde_macros/Cargo.toml
+++ b/serde_macros/Cargo.toml
@@ -17,6 +17,7 @@ plugin = true
 
 [features]
 unstable-testing = [
+    "clippy",
     "skeptic",
     "serde_json",
     "serde/unstable-testing",
diff --git a/serde_macros/tests/run-pass/identity-op.rs b/serde_macros/tests/run-pass/identity-op.rs
index a82f100d..dcf8117a 100644
--- a/serde_macros/tests/run-pass/identity-op.rs
+++ b/serde_macros/tests/run-pass/identity-op.rs
@@ -1,5 +1,5 @@
 #![feature(custom_derive, plugin)]
-#![plugin(serde_macros)]
+#![plugin(serde_macros, clippy)]
 
 #![deny(identity_op)]
 
diff --git a/testing/Cargo.toml b/testing/Cargo.toml
index 471ac26d..2604154c 100644
--- a/testing/Cargo.toml
+++ b/testing/Cargo.toml
@@ -12,7 +12,7 @@ keywords = ["serialization"]
 build = "build.rs"
 
 [features]
-unstable-testing = ["serde/unstable-testing", "serde_codegen/unstable-testing"]
+unstable-testing = ["clippy", "serde/unstable-testing", "serde_codegen/unstable-testing"]
 
 [build-dependencies]
 serde_codegen = { path = "../serde_codegen", features = ["with-syntex"] }