diff --git a/src/numeric/impl_numeric.rs b/src/numeric/impl_numeric.rs
index cff10c863..89a927b18 100644
--- a/src/numeric/impl_numeric.rs
+++ b/src/numeric/impl_numeric.rs
@@ -7,7 +7,7 @@
 // except according to those terms.
 
 use std::ops::{Add, Div, Mul};
-use libnum::{self, One, Zero, Float, FromPrimitive};
+use libnum::{self, Zero, Float, FromPrimitive};
 use itertools::free::enumerate;
 
 use imp_prelude::*;
@@ -123,8 +123,9 @@ impl<A, S, D> ArrayBase<S, D>
 
     /// Return mean along `axis`.
     ///
-    /// **Panics** if `axis` is out of bounds or if the length of the axis is
-    /// zero and division by zero panics for type `A`.
+    /// **Panics** if `axis` is out of bounds, if the length of the axis is
+    /// zero and division by zero panics for type `A`, or if `A::from_usize()`
+    /// fails for the axis length.
     ///
     /// ```
     /// use ndarray::{aview1, arr2, Axis};
@@ -137,16 +138,12 @@ impl<A, S, D> ArrayBase<S, D>
     /// );
     /// ```
     pub fn mean_axis(&self, axis: Axis) -> Array<A, D::Smaller>
-        where A: Clone + Zero + One + Add<Output=A> + Div<Output=A>,
+        where A: Clone + Zero + FromPrimitive + Add<Output=A> + Div<Output=A>,
               D: RemoveAxis,
     {
-        let n = self.len_of(axis);
+        let n = A::from_usize(self.len_of(axis)).expect("Converting axis length to `A` must not fail.");
         let sum = self.sum_axis(axis);
-        let mut cnt = A::zero();
-        for _ in 0..n {
-            cnt = cnt + A::one();
-        }
-        sum / &aview0(&cnt)
+        sum / &aview0(&n)
     }
 
     /// Return variance along `axis`.