diff --git a/src/libstd/num/i64.rs b/src/libstd/num/i64.rs
index 10df7e37b88..d991bf03300 100644
--- a/src/libstd/num/i64.rs
+++ b/src/libstd/num/i64.rs
@@ -10,7 +10,9 @@
 
 //! Operations and constants for `i64`
 
-use num::{BitCount, CheckedAdd, CheckedSub, CheckedMul};
+use num::{BitCount, CheckedAdd, CheckedSub};
+#[cfg(target_word_size = "64")]
+use num::CheckedMul;
 use option::{Option, Some, None};
 use unstable::intrinsics;
 
diff --git a/src/libstd/num/u64.rs b/src/libstd/num/u64.rs
index b311183ba11..d3077333077 100644
--- a/src/libstd/num/u64.rs
+++ b/src/libstd/num/u64.rs
@@ -10,7 +10,9 @@
 
 //! Operations and constants for `u64`
 
-use num::{CheckedAdd, CheckedSub, CheckedMul};
+use num::{CheckedAdd, CheckedSub};
+#[cfg(target_word_size = "64")]
+use num::CheckedMul;
 use option::{Option, Some, None};
 use unstable::intrinsics;