diff --git a/lib/mimemagic.rb b/lib/mimemagic.rb
index 3be35a1..9b28d1b 100644
--- a/lib/mimemagic.rb
+++ b/lib/mimemagic.rb
@@ -109,28 +109,27 @@ def self.child?(child, parent)
   end
 
   def self.magic_match(io, method)
-    if io.respond_to?(:seek) && io.respond_to?(:read)
-      io.binmode
-      io.set_encoding(Encoding::BINARY) if io.respond_to?(:set_encoding)
-      buffer = "".force_encoding(Encoding::BINARY)
-      MAGIC.send(method) { |type, matches| magic_match_io(io, matches, buffer) }
-    else
-      str = io.respond_to?(:read) ? io.read : io.to_s
-      magic_match(StringIO.new(str), method)
-    end
+    return magic_match(StringIO.new(io.to_s), method) unless io.respond_to?(:read)
+
+    io.binmode if io.respond_to?(:binmode)
+    io.set_encoding(Encoding::BINARY) if io.respond_to?(:set_encoding)
+    buffer = "".force_encoding(Encoding::BINARY)
+
+    MAGIC.send(method) { |type, matches| magic_match_io(io, matches, buffer) }
   end
 
   def self.magic_match_io(io, matches, buffer)
     matches.any? do |offset, value, children|
       match =
         if Range === offset
-          io.seek(offset.begin)
+          io.read(offset.begin, buffer)
           x = io.read(offset.end - offset.begin + value.bytesize, buffer)
           x && x.include?(value)
         else
-          io.seek(offset)
+          io.read(offset, buffer)
           io.read(value.bytesize, buffer) == value
         end
+      io.rewind
       match && (!children || magic_match_io(io, children, buffer))
     end
   end
diff --git a/test/mimemagic_test.rb b/test/mimemagic_test.rb
index 6cdb386..7ac11b0 100644
--- a/test/mimemagic_test.rb
+++ b/test/mimemagic_test.rb
@@ -1,6 +1,7 @@
 require 'bacon'
 require 'mimemagic'
 require 'stringio'
+require 'forwardable'
 
 describe 'MimeMagic' do
   it 'should have type, mediatype and subtype' do
@@ -116,12 +117,15 @@
 
   it 'should handle different file objects' do
     MimeMagic.add('application/mimemagic-test', magic: [[0, 'MAGICTEST']])
-    class ReadableObj
-      def read
-        'MAGICTEST'
+    class IOObject
+      def initialize
+        @io = StringIO.new('MAGICTEST')
       end
+
+      extend Forwardable
+      delegate [:read, :size, :rewind, :eof?, :close] => :@io
     end
-    MimeMagic.by_magic(ReadableObj.new).should.equal 'application/mimemagic-test'
+    MimeMagic.by_magic(IOObject.new).should.equal 'application/mimemagic-test'
     class StringableObject
       def to_s
         'MAGICTEST'