diff --git a/library/std/src/f32.rs b/library/std/src/f32.rs
index 776899dbcfd..c3506175715 100644
--- a/library/std/src/f32.rs
+++ b/library/std/src/f32.rs
@@ -989,7 +989,9 @@ impl f32 {
         unsafe { cmath::tgammaf(self) }
     }
 
-    /// Returns the natural logarithm of the gamma function.
+    /// Natural logarithm of the absolute value of the gamma function
+    ///
+    /// The integer part of the tuple indicates the sign of the gamma function.
     ///
     /// # Examples
     ///
diff --git a/library/std/src/f64.rs b/library/std/src/f64.rs
index 4f4f5f02471..e4b7bfeeb84 100644
--- a/library/std/src/f64.rs
+++ b/library/std/src/f64.rs
@@ -989,7 +989,9 @@ impl f64 {
         unsafe { cmath::tgamma(self) }
     }
 
-    /// Returns the natural logarithm of the gamma function.
+    /// Natural logarithm of the absolute value of the gamma function
+    ///
+    /// The integer part of the tuple indicates the sign of the gamma function.
     ///
     /// # Examples
     ///