diff --git a/lib/fluent/plugin/in_tail.rb b/lib/fluent/plugin/in_tail.rb
index 852f2723bd..703d9d01c1 100644
--- a/lib/fluent/plugin/in_tail.rb
+++ b/lib/fluent/plugin/in_tail.rb
@@ -1056,8 +1056,9 @@ def read_lines(lines)
             # Using freeze and slice is faster than slice!
             # See https://github.com/fluent/fluentd/pull/2527
             @buffer.freeze
-            rbuf = @buffer.slice(0, idx + 1)
-            @buffer = @buffer.slice(idx + 1, @buffer.size)
+            slice_position = idx + 1
+            rbuf = @buffer.slice(0, slice_position)
+            @buffer = @buffer.slice(slice_position, @buffer.size - slice_position)
             idx = @buffer.index(@eol)
 
             is_long_line = @max_line_size && (