diff --git a/spec/common_exception_handler_spec.cr b/spec/common_exception_handler_spec.cr
index 5442306..75ff2e9 100644
--- a/spec/common_exception_handler_spec.cr
+++ b/spec/common_exception_handler_spec.cr
@@ -7,7 +7,7 @@ describe "Kemal::CommonExceptionHandler" do
     end
 
     request = HTTP::Request.new("GET", "/asd")
-    io = MemoryIO.new
+    io = IO::Memory.new
     response = HTTP::Server::Response.new(io)
     context = HTTP::Server::Context.new(request, response)
     Kemal::CommonExceptionHandler::INSTANCE.call(context)
@@ -25,7 +25,7 @@ describe "Kemal::CommonExceptionHandler" do
       env.response.status_code = 403
     end
     request = HTTP::Request.new("GET", "/")
-    io = MemoryIO.new
+    io = IO::Memory.new
     response = HTTP::Server::Response.new(io)
     context = HTTP::Server::Context.new(request, response)
     Kemal::CommonExceptionHandler::INSTANCE.next = Kemal::RouteHandler::INSTANCE
@@ -46,7 +46,7 @@ describe "Kemal::CommonExceptionHandler" do
       env.response.status_code = 500
     end
     request = HTTP::Request.new("GET", "/")
-    io = MemoryIO.new
+    io = IO::Memory.new
     response = HTTP::Server::Response.new(io)
     context = HTTP::Server::Context.new(request, response)
     Kemal::CommonExceptionHandler::INSTANCE.next = Kemal::RouteHandler::INSTANCE
@@ -68,7 +68,7 @@ describe "Kemal::CommonExceptionHandler" do
       env.response.status_code = 500
     end
     request = HTTP::Request.new("GET", "/")
-    io = MemoryIO.new
+    io = IO::Memory.new
     response = HTTP::Server::Response.new(io)
     context = HTTP::Server::Context.new(request, response)
     Kemal::CommonExceptionHandler::INSTANCE.next = Kemal::RouteHandler::INSTANCE
@@ -90,7 +90,7 @@ describe "Kemal::CommonExceptionHandler" do
       env.response.status_code = 500
     end
     request = HTTP::Request.new("GET", "/")
-    io = MemoryIO.new
+    io = IO::Memory.new
     response = HTTP::Server::Response.new(io)
     context = HTTP::Server::Context.new(request, response)
     Kemal::CommonExceptionHandler::INSTANCE.next = Kemal::RouteHandler::INSTANCE
diff --git a/spec/common_log_handler_spec.cr b/spec/common_log_handler_spec.cr
index 840c79d..1e4585c 100644
--- a/spec/common_log_handler_spec.cr
+++ b/spec/common_log_handler_spec.cr
@@ -3,7 +3,7 @@ require "./spec_helper"
 describe "Kemal::CommonLogHandler" do
   it "logs to the given IO" do
     config = Kemal.config
-    io = MemoryIO.new
+    io = IO::Memory.new
     logger = Kemal::CommonLogHandler.new io
     logger.write "Something"
     io.to_s.should eq "Something"
@@ -11,8 +11,8 @@ describe "Kemal::CommonLogHandler" do
 
   it "creates log message for each request" do
     request = HTTP::Request.new("GET", "/")
-    io = MemoryIO.new
-    context_io = MemoryIO.new
+    io = IO::Memory.new
+    context_io = IO::Memory.new
     response = HTTP::Server::Response.new(context_io)
     context = HTTP::Server::Context.new(request, response)
     logger = Kemal::CommonLogHandler.new io
diff --git a/spec/context_spec.cr b/spec/context_spec.cr
index af8cc1d..b9e9003 100644
--- a/spec/context_spec.cr
+++ b/spec/context_spec.cr
@@ -49,7 +49,7 @@ describe "Context" do
       }
     end
     request = HTTP::Request.new("GET", "/")
-    io = MemoryIO.new
+    io = IO::Memory.new
     response = HTTP::Server::Response.new(io)
     context = HTTP::Server::Context.new(request, response)
     Kemal::Middleware::Filter::INSTANCE.call(context)
diff --git a/spec/init_handler_spec.cr b/spec/init_handler_spec.cr
index 9639474..d877249 100644
--- a/spec/init_handler_spec.cr
+++ b/spec/init_handler_spec.cr
@@ -3,7 +3,7 @@ require "./spec_helper"
 describe "Kemal::InitHandler" do
   it "initializes context with Content-Type: text/html" do
     request = HTTP::Request.new("GET", "/")
-    io = MemoryIO.new
+    io = IO::Memory.new
     response = HTTP::Server::Response.new(io)
     context = HTTP::Server::Context.new(request, response)
     Kemal::InitHandler::INSTANCE.next = ->(context : HTTP::Server::Context) {}
@@ -13,7 +13,7 @@ describe "Kemal::InitHandler" do
 
   it "initializes context with X-Powered-By: Kemal" do
     request = HTTP::Request.new("GET", "/")
-    io = MemoryIO.new
+    io = IO::Memory.new
     response = HTTP::Server::Response.new(io)
     context = HTTP::Server::Context.new(request, response)
     Kemal::InitHandler::INSTANCE.call(context)
diff --git a/spec/middleware/csrf_spec.cr b/spec/middleware/csrf_spec.cr
index 62aae20..198c4b4 100644
--- a/spec/middleware/csrf_spec.cr
+++ b/spec/middleware/csrf_spec.cr
@@ -62,7 +62,7 @@ describe "Kemal::Middleware::CSRF" do
 end
 
 def process_request(handler, request)
-  io = MemoryIO.new
+  io = IO::Memory.new
   response = HTTP::Server::Response.new(io)
   context = HTTP::Server::Context.new(request, response)
   handler.call(context)
diff --git a/spec/spec_helper.cr b/spec/spec_helper.cr
index 4eb469d..9c2b488 100644
--- a/spec/spec_helper.cr
+++ b/spec/spec_helper.cr
@@ -13,7 +13,7 @@ class CustomLogHandler < Kemal::BaseLogHandler
 end
 
 def create_request_and_return_io(handler, request)
-  io = MemoryIO.new
+  io = IO::Memory.new
   response = HTTP::Server::Response.new(io)
   context = HTTP::Server::Context.new(request, response)
   handler.call(context)
@@ -23,20 +23,20 @@ def create_request_and_return_io(handler, request)
 end
 
 def create_ws_request_and_return_io(handler, request)
-  io = MemoryIO.new
+  io = IO::Memory.new
   response = HTTP::Server::Response.new(io)
   context = HTTP::Server::Context.new(request, response)
   begin
     handler.call context
   rescue IO::Error
-    # Raises because the MemoryIO is empty
+    # Raises because the IO::Memory is empty
   end
   response.close
   io
 end
 
 def call_request_on_app(request)
-  io = MemoryIO.new
+  io = IO::Memory.new
   response = HTTP::Server::Response.new(io)
   context = HTTP::Server::Context.new(request, response)
   main_handler = build_main_handler
diff --git a/spec/static_file_handler.cr b/spec/static_file_handler.cr
index 31ce94f..0861018 100644
--- a/spec/static_file_handler.cr
+++ b/spec/static_file_handler.cr
@@ -1,7 +1,7 @@
 require "./spec_helper"
 
 private def handle(request, fallthrough = true)
-  io = MemoryIO.new
+  io = IO::Memory.new
   response = HTTP::Server::Response.new(io)
   context = HTTP::Server::Context.new(request, response)
   handler = Kemal::StaticFileHandler.new "#{__DIR__}/static", fallthrough
diff --git a/src/kemal/helpers/macros.cr b/src/kemal/helpers/macros.cr
index 2f9b978..d263858 100644
--- a/src/kemal/helpers/macros.cr
+++ b/src/kemal/helpers/macros.cr
@@ -33,7 +33,7 @@ CONTENT_FOR_BLOCKS = Hash(String, Tuple(String, Proc(String))).new
 # setting the appropriate set of tags that should be added to the layout.
 macro content_for(key, file = __FILE__)
   %proc = ->() {
-    __kilt_io__ = MemoryIO.new
+    __kilt_io__ = IO::Memory.new
     {{ yield }}
     __kilt_io__.to_s
   }