diff --git a/lib/grape.rb b/lib/grape.rb
index 680bea819f..f4ec5701fa 100644
--- a/lib/grape.rb
+++ b/lib/grape.rb
@@ -42,6 +42,10 @@ def self.deprecator
     @deprecator ||= ActiveSupport::Deprecation.new('2.0', 'Grape')
   end
 
+  def self.rack3?
+    Gem::Version.new(::Rack.release) >= Gem::Version.new('3')
+  end
+
   eager_autoload do
     autoload :API
     autoload :Endpoint
diff --git a/lib/grape/http/headers.rb b/lib/grape/http/headers.rb
index 3014ccff0d..e8a368b82c 100644
--- a/lib/grape/http/headers.rb
+++ b/lib/grape/http/headers.rb
@@ -11,15 +11,7 @@ module Headers
       REQUEST_METHOD  = 'REQUEST_METHOD'
       QUERY_STRING    = 'QUERY_STRING'
 
-      if Gem::Version.new(Rack.release) < Gem::Version.new('3')
-        ALLOW             = 'Allow'
-        CACHE_CONTROL     = 'Cache-Control'
-        CONTENT_LENGTH    = 'Content-Length'
-        CONTENT_TYPE      = 'Content-Type'
-        LOCATION          = 'Location'
-        TRANSFER_ENCODING = 'Transfer-Encoding'
-        X_CASCADE         = 'X-Cascade'
-      else
+      if Grape.rack3?
         ALLOW             = 'allow'
         CACHE_CONTROL     = 'cache-control'
         CONTENT_LENGTH    = 'content-length'
@@ -27,6 +19,14 @@ module Headers
         LOCATION          = 'location'
         TRANSFER_ENCODING = 'transfer-encoding'
         X_CASCADE         = 'x-cascade'
+      else
+        ALLOW = 'Allow'
+        CACHE_CONTROL     = 'Cache-Control'
+        CONTENT_LENGTH    = 'Content-Length'
+        CONTENT_TYPE      = 'Content-Type'
+        LOCATION          = 'Location'
+        TRANSFER_ENCODING = 'Transfer-Encoding'
+        X_CASCADE         = 'X-Cascade'
       end
 
       GET     = 'GET'
diff --git a/lib/grape/request.rb b/lib/grape/request.rb
index 669f04f413..f522ea923b 100644
--- a/lib/grape/request.rb
+++ b/lib/grape/request.rb
@@ -46,12 +46,14 @@ def build_headers
       end
     end
 
-    def transform_header(header)
-      if Gem::Version.new(Rack.release) < Gem::Version.new('3')
-        -header[5..].split('_').map(&:capitalize).join('-')
-      else
+    if Grape.rack3?
+      def transform_header(header)
         -header[5..].tr('_', '-').downcase
       end
+    else
+      def transform_header(header)
+        -header[5..].split('_').map(&:capitalize).join('-')
+      end
     end
   end
 end