diff --git a/autoload/indent_guides.vim b/autoload/indent_guides.vim
index 2ac36d2..5ada70d 100644
--- a/autoload/indent_guides.vim
+++ b/autoload/indent_guides.vim
@@ -179,7 +179,7 @@ function! indent_guides#init_script_vars()
   let s:debug             = g:indent_guides_debug
   let s:indent_levels     = g:indent_guides_indent_levels
   let s:auto_colors       = g:indent_guides_auto_colors
-  let s:change_percent    = g:indent_guides_color_change_percent / 100.0
+  let s:change_percent    = g:indent_guides_color_change_percent / str2float("100.0")
   let s:color_hex_pat     = g:indent_guides_color_hex_pattern
   let s:color_hex_bg_pat  = g:indent_guides_color_hex_guibg_pattern
   let s:color_name_bg_pat = g:indent_guides_color_name_guibg_pattern