diff --git a/src/libcore/num/f32.rs b/src/libcore/num/f32.rs
index 718dd42a61535..65332d4b97acc 100644
--- a/src/libcore/num/f32.rs
+++ b/src/libcore/num/f32.rs
@@ -33,7 +33,11 @@ pub const MANTISSA_DIGITS: u32 = 24;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub const DIGITS: u32 = 6;
 
-/// Difference between `1.0` and the next largest representable number.
+/// [Machine epsilon] value for `f32`.
+///
+/// This is the difference between `1.0` and the next largest representable number.
+///
+/// [Machine epsilon]: https://en.wikipedia.org/wiki/Machine_epsilon
 #[stable(feature = "rust1", since = "1.0.0")]
 pub const EPSILON: f32 = 1.19209290e-07_f32;
 
diff --git a/src/libcore/num/f64.rs b/src/libcore/num/f64.rs
index f128c55c78afa..c9a643e7b334d 100644
--- a/src/libcore/num/f64.rs
+++ b/src/libcore/num/f64.rs
@@ -33,7 +33,11 @@ pub const MANTISSA_DIGITS: u32 = 53;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub const DIGITS: u32 = 15;
 
-/// Difference between `1.0` and the next largest representable number.
+/// [Machine epsilon] value for `f64`.
+///
+/// This is the difference between `1.0` and the next largest representable number.
+///
+/// [Machine epsilon]: https://en.wikipedia.org/wiki/Machine_epsilon
 #[stable(feature = "rust1", since = "1.0.0")]
 pub const EPSILON: f64 = 2.2204460492503131e-16_f64;