diff --git a/lib/bigdecimal/math.rb b/lib/bigdecimal/math.rb
index 83bba449..38286944 100644
--- a/lib/bigdecimal/math.rb
+++ b/lib/bigdecimal/math.rb
@@ -585,6 +585,7 @@ def expm1(x, prec)
     exp(x, exp_prec).sub(1, prec)
   end
 
+  # call-seq:
   #   erf(decimal, numeric) -> BigDecimal
   #
   # Computes the error function of +decimal+ to the specified number of digits of