diff --git a/bigint/src/lib.rs b/bigint/src/lib.rs
index 5257e3a..74d7576 100644
--- a/bigint/src/lib.rs
+++ b/bigint/src/lib.rs
@@ -72,6 +72,8 @@
 
 #[cfg(any(feature = "rand", test))]
 extern crate rand;
+#[cfg(feature = "serde")]
+extern crate serde;
 
 extern crate num_integer as integer;
 extern crate num_traits as traits;