diff --git a/rational/src/lib.rs b/rational/src/lib.rs
index e12b987..c2d58e4 100644
--- a/rational/src/lib.rs
+++ b/rational/src/lib.rs
@@ -668,6 +668,7 @@ impl RatioErrorKind {
     }
 }
 
+#[cfg(feature = "num-bigint")]
 impl FromPrimitive for Ratio<BigInt> {
     fn from_i64(n: i64) -> Option<Self> {
         Some(Ratio::from_integer(n.into()))