diff --git a/mrbgems/mruby-math/src/math.c b/mrbgems/mruby-math/src/math.c
index 26a6eaa40..76ee57481 100644
--- a/mrbgems/mruby-math/src/math.c
+++ b/mrbgems/mruby-math/src/math.c
@@ -74,7 +74,7 @@ atanh(double x)
   }
   else {
     /* Basic formula for atanh */
-    y = 0.5 * (log(1.0+x) - log(1.0-x));
+    y = 0.5 * (log1p(x) - log1p(-x));
   }
 
   return y;