diff --git a/lib/SVG/Graph/TimeSeries.rb b/lib/SVG/Graph/TimeSeries.rb
index bfa7c96..e6a3a0f 100644
--- a/lib/SVG/Graph/TimeSeries.rb
+++ b/lib/SVG/Graph/TimeSeries.rb
@@ -171,7 +171,7 @@ module SVG
       protected
 
       def min_x_value=(value)
-        @min_x_value = DateTime.parse( data[:data][i] ).to_time
+        @min_x_value = DateTime.parse( value ).to_time
       end