diff --git a/library/core/src/num/f32.rs b/library/core/src/num/f32.rs
index 3144db197074b..290f649f9acd6 100644
--- a/library/core/src/num/f32.rs
+++ b/library/core/src/num/f32.rs
@@ -957,6 +957,7 @@ impl f32 {
         } else if self == other {
             if self.is_sign_negative() && other.is_sign_positive() { self } else { other }
         } else {
+            // At least one input is NaN. Use `+` to perform NaN propagation and quieting.
             self + other
         }
     }
diff --git a/library/core/src/num/f64.rs b/library/core/src/num/f64.rs
index 20833defc41b8..7569d2cd6ca97 100644
--- a/library/core/src/num/f64.rs
+++ b/library/core/src/num/f64.rs
@@ -968,6 +968,7 @@ impl f64 {
         } else if self == other {
             if self.is_sign_negative() && other.is_sign_positive() { self } else { other }
         } else {
+            // At least one input is NaN. Use `+` to perform NaN propagation and quieting.
             self + other
         }
     }