diff --git a/ChangeLog b/ChangeLog
index d1dd7d7f76..cdfd4cb3a3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Oct 26 18:51:00 2010  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* lib/scanf.rb (extract_float): allow 2.e+2 style.
+	  [ruby-dev:42452] #3978
+
 Tue Oct 26 18:09:36 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* Makefile.in (ASFLAGS): needs INCFLAGS.
diff --git a/lib/scanf.rb b/lib/scanf.rb
index dd6ba6c9d0..50eefbcd2d 100644
--- a/lib/scanf.rb
+++ b/lib/scanf.rb
@@ -321,6 +321,8 @@ module Scanf
           end
         end
         (sign == ?- ? -1 : 1) * Math.ldexp(f, exp.to_i)
+      elsif /\A([-+]?\d+)\.([eE][-+]\d+)/ =~ s
+        ($1 << $2).to_f
       else
         s.to_f
       end