diff --git a/lib/rack/multipart/parser.rb b/lib/rack/multipart/parser.rb
index ec2658419..98eceaa15 100644
--- a/lib/rack/multipart/parser.rb
+++ b/lib/rack/multipart/parser.rb
@@ -125,7 +125,7 @@ def get_filename(head)
           filename = $1
         end
 
-        if filename && filename.scan(/%..?/).all? { |s| s =~ /%[0-9a-fA-F]{2}/ }
+        if filename && filename.scan(/%.?.?/).all? { |s| s =~ /%[0-9a-fA-F]{2}/ }
           filename = Utils.unescape(filename)
         end
         if filename && filename !~ /\\[^\\"]/
diff --git a/test/multipart/filename_with_unescaped_percentages3 b/test/multipart/filename_with_unescaped_percentages3
new file mode 100644
index 000000000..4dba3c885
--- /dev/null
+++ b/test/multipart/filename_with_unescaped_percentages3
@@ -0,0 +1,6 @@
+------WebKitFormBoundary2NHc7OhsgU68l3Al
+Content-Disposition: form-data; name="document[attachment]"; filename="100%"
+Content-Type: image/jpeg
+
+contents
+------WebKitFormBoundary2NHc7OhsgU68l3Al--
diff --git a/test/spec_multipart.rb b/test/spec_multipart.rb
index c70cd7ee6..b0bf57c08 100644
--- a/test/spec_multipart.rb
+++ b/test/spec_multipart.rb
@@ -241,6 +241,21 @@ def multipart_file(name)
     files[:tempfile].read.should.equal "contents"
   end
 
+  should "parse filename with unescaped percentage characters that look like partial hex escapes" do
+    env = Rack::MockRequest.env_for("/", multipart_fixture(:filename_with_unescaped_percentages3, "----WebKitFormBoundary2NHc7OhsgU68l3Al"))
+    params = Rack::Multipart.parse_multipart(env)
+    files = params["document"]["attachment"]
+    files[:type].should.equal "image/jpeg"
+    files[:filename].should.equal "100%"
+    files[:head].should.equal <<-MULTIPART
+Content-Disposition: form-data; name="document[attachment]"; filename="100%"\r
+Content-Type: image/jpeg\r
+    MULTIPART
+
+    files[:name].should.equal "document[attachment]"
+    files[:tempfile].read.should.equal "contents"
+  end
+
   it "rewinds input after parsing upload" do
     options = multipart_fixture(:text)
     input = options[:input]