diff --git a/lib/uri/common.rb b/lib/uri/common.rb
index 8b9e1e3695..f23fe98d4f 100644
--- a/lib/uri/common.rb
+++ b/lib/uri/common.rb
@@ -984,7 +984,7 @@ module URI
   # See URI.decode_www_form_component, URI.encode_www_form
   def self.decode_www_form(str, enc=Encoding::UTF_8)
     return [] if str.empty?
-    unless /\A#{WFKV_}*=#{WFKV_}*(?:[;&]#{WFKV_}*=#{WFKV_}*)*\z/o =~ str
+    unless /\A#{WFKV_}=#{WFKV_}(?:[;&]#{WFKV_}=#{WFKV_})*\z/o =~ str
       raise ArgumentError, "invalid data of application/x-www-form-urlencoded (#{str})"
     end
     ary = []