diff --git a/src/conf.rs b/src/conf.rs
index 0ceede3b5..93caa1edc 100644
--- a/src/conf.rs
+++ b/src/conf.rs
@@ -100,6 +100,10 @@ macro_rules! define_Conf {
                             }
                         },
                     )+
+                    "third-party" => {
+                        // for external tools such as clippy-service
+                        return Ok(());
+                    }
                     _ => {
                         return Err(ConfError::UnknownKey(name));
                     }
diff --git a/tests/compile-fail/conf_unknown_key.toml b/tests/compile-fail/conf_unknown_key.toml
index df298ea78..554b87cc5 100644
--- a/tests/compile-fail/conf_unknown_key.toml
+++ b/tests/compile-fail/conf_unknown_key.toml
@@ -1 +1,6 @@
+# that one is an error
 foobar = 42
+
+# that one is white-listed
+[third-party]
+clippy-feature = "nightly"
diff --git a/tests/run-pass/conf_unknown_key.rs b/tests/run-pass/conf_unknown_key.rs
new file mode 100644
index 000000000..bb186d476
--- /dev/null
+++ b/tests/run-pass/conf_unknown_key.rs
@@ -0,0 +1,4 @@
+#![feature(plugin)]
+#![plugin(clippy(conf_file="./tests/run-pass/conf_unknown_key.toml"))]
+
+fn main() {}
diff --git a/tests/run-pass/conf_unknown_key.toml b/tests/run-pass/conf_unknown_key.toml
new file mode 100644
index 000000000..9f87de20b
--- /dev/null
+++ b/tests/run-pass/conf_unknown_key.toml
@@ -0,0 +1,3 @@
+# this is ignored by Clippy, but allowed for other tools like clippy-service
+[third-party]
+clippy-feature = "nightly"