diff --git a/src/libstd/f32.rs b/src/libstd/f32.rs
index 26644c769575c..4f4baf1e8cd91 100644
--- a/src/libstd/f32.rs
+++ b/src/libstd/f32.rs
@@ -195,8 +195,10 @@ impl f32 {
     }
 
     /// Fused multiply-add. Computes `(self * a) + b` with only one rounding
-    /// error. This produces a more accurate result with better performance than
-    /// a separate multiplication operation followed by an add.
+    /// error, yielding a more accurate result than an unfused multiply-add.
+    ///
+    /// Using `mul_add` can be more performant than an unfused multiply-add if
+    /// the target architecture has a dedicated `fma` CPU instruction.
     ///
     /// ```
     /// use std::f32;
diff --git a/src/libstd/f64.rs b/src/libstd/f64.rs
index a7e63f59b1c67..e00ff60452dd0 100644
--- a/src/libstd/f64.rs
+++ b/src/libstd/f64.rs
@@ -173,8 +173,10 @@ impl f64 {
     }
 
     /// Fused multiply-add. Computes `(self * a) + b` with only one rounding
-    /// error. This produces a more accurate result with better performance than
-    /// a separate multiplication operation followed by an add.
+    /// error, yielding a more accurate result than an unfused multiply-add.
+    ///
+    /// Using `mul_add` can be more performant than an unfused multiply-add if
+    /// the target architecture has a dedicated `fma` CPU instruction.
     ///
     /// ```
     /// let m = 10.0_f64;