diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index d533310625e59..c5175287ccfa6 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -131,6 +131,10 @@ macro_rules! int_impl {
         ///
         /// Leading and trailing whitespace represent an error.
         ///
+        /// # Panics
+        ///
+        /// This function panics if `radix` is not in the range from 2 to 36.
+        ///
         /// # Examples
         ///
         /// Basic usage: