diff --git a/lib/daru/dataframe.rb b/lib/daru/dataframe.rb
index 6f93e1f7f..55a6b63a2 100644
--- a/lib/daru/dataframe.rb
+++ b/lib/daru/dataframe.rb
@@ -3096,7 +3096,7 @@ def coerce_positions *positions, size
         when Range
           size.times.to_a[positions.first]
         else
-          raise ArgumentError, 'Unkown position type.'
+          raise ArgumentError, 'Unknown position type.'
         end
       else
         positions