diff --git a/lib/sisimai/string.rb b/lib/sisimai/string.rb
index 107db0ff..d3d993ac 100644
--- a/lib/sisimai/string.rb
+++ b/lib/sisimai/string.rb
@@ -66,8 +66,8 @@ def to_plain(argv1 = '', loose = false)
           # 3. <a href = 'http://...'>...</a> to " http://... "
           # 4. <a href = 'mailto:...'>...</a> to " Value <mailto:...> "
           plain.scrub!('?')
-          plain.gsub!(%r|<head>.+</head>|im, '')
-          plain.gsub!(%r|<style.+?>.+</style>|im, '')
+          plain.gsub!(%r|<head>.*?</head>|im, '')
+          plain.gsub!(%r|<style.*?>.*?</style>|im, '')
           plain.gsub!(%r|<a\s+href\s*=\s*['"](https?://.+?)['"].*?>(.*?)</a>|i, '[\2](\1)')
           plain.gsub!(%r|<a\s+href\s*=\s*["']mailto:([^\s]+?)["']>(.*?)</a>|i, '[\2](mailto:\1)')
 
