diff --git a/lib/grape/http/headers.rb b/lib/grape/http/headers.rb
index 96a5e4aaf3..314334b0ae 100644
--- a/lib/grape/http/headers.rb
+++ b/lib/grape/http/headers.rb
@@ -11,7 +11,7 @@ module Headers
       REQUEST_METHOD  = 'REQUEST_METHOD'
       QUERY_STRING    = 'QUERY_STRING'
 
-      if Gem::Version.new(Rack::RELEASE) < Gem::Version.new('3')
+      if Gem::Version.new(Rack.release) < Gem::Version.new('3')
         CONTENT_TYPE = 'Content-Type'
         X_CASCADE    = 'X-Cascade'
       else