diff --git a/spec/std/http/client/client_spec.cr b/spec/std/http/client/client_spec.cr
index a1bc5dedc19e..2c3285a61512 100644
--- a/spec/std/http/client/client_spec.cr
+++ b/spec/std/http/client/client_spec.cr
@@ -87,5 +87,13 @@ module HTTP
         client.get("/")
       end
     end
+
+    it "accepts IO objects as body" do
+      body = MemoryIO.new("hello world")
+
+      TestServer.open("localhost", 0, 0) do |server|
+        Client.exec("POST", "http://localhost:#{server.addr.ip_port}/", nil, body)
+      end
+    end
   end
 end
diff --git a/spec/std/http/request_spec.cr b/spec/std/http/request_spec.cr
index 9114ad95d181..580d107faac1 100644
--- a/spec/std/http/request_spec.cr
+++ b/spec/std/http/request_spec.cr
@@ -66,6 +66,14 @@ module HTTP
       io.to_s.should eq("POST / HTTP/1.1\r\nContent-Length: 13\r\n\r\nthisisthebody")
     end
 
+    it "serialize chunked POST (with IO as body)" do
+      body = MemoryIO.new "hello world"
+      request = Request.new "POST", "/", body: body
+      io = MemoryIO.new
+      request.to_io(io)
+      io.to_s.should eq("POST / HTTP/1.1\r\nTransfer-Encoding: chunked\r\n\r\nb\r\nhello world\r\n0\r\n\r\n")
+    end
+
     it "parses GET" do
       request = Request.from_io(MemoryIO.new("GET / HTTP/1.1\r\nHost: host.example.org\r\n\r\n")).not_nil!
       request.method.should eq("GET")
diff --git a/src/http/client/client.cr b/src/http/client/client.cr
index 8df60bc0ce17..b84b4e28daf3 100644
--- a/src/http/client/client.cr
+++ b/src/http/client/client.cr
@@ -193,7 +193,7 @@ class HTTP::Client
     # response = client.{{method.id}}("/", headers: HTTP::Headers{"User-agent": "AwesomeApp"}, body: "Hello!")
     # response.body #=> "..."
     # ```
-    def {{method.id}}(path, headers = nil : HTTP::Headers?, body = nil : String?) : HTTP::Client::Response
+    def {{method.id}}(path, headers = nil : HTTP::Headers?, body = nil : String | IO | Nil) : HTTP::Client::Response
       exec {{method.upcase}}, path, headers, body
     end
 
@@ -206,7 +206,7 @@ class HTTP::Client
     #   response.body_io.gets #=> "..."
     # end
     # ```
-    def {{method.id}}(path, headers = nil : HTTP::Headers?, body = nil : String?)
+    def {{method.id}}(path, headers = nil : HTTP::Headers?, body = nil : String | IO | Nil)
       exec {{method.upcase}}, path, headers, body do |response|
         yield response
       end
@@ -219,7 +219,7 @@ class HTTP::Client
     # response = HTTP::Client.{{method.id}}("/", headers: HTTP::Headers{"User-agent": "AwesomeApp"}, body: "Hello!")
     # response.body #=> "..."
     # ```
-    def self.{{method.id}}(url : String | URI, headers = nil : HTTP::Headers?, body = nil : String?) : HTTP::Client::Response
+    def self.{{method.id}}(url : String | URI, headers = nil : HTTP::Headers?, body = nil : String | IO | Nil) : HTTP::Client::Response
       exec {{method.upcase}}, url, headers, body
     end
 
@@ -231,7 +231,7 @@ class HTTP::Client
     #   response.body_io.gets #=> "..."
     # end
     # ```
-    def self.{{method.id}}(url : String | URI, headers = nil : HTTP::Headers?, body = nil : String?)
+    def self.{{method.id}}(url : String | URI, headers = nil : HTTP::Headers?, body = nil : String | IO | Nil)
       exec {{method.upcase}}, url, headers, body do |response|
         yield response
       end
@@ -348,7 +348,7 @@ class HTTP::Client
   # response = client.exec "GET", "/"
   # response.body # => "..."
   # ```
-  def exec(method : String, path, headers = nil : HTTP::Headers?, body = nil : String?) : HTTP::Client::Response
+  def exec(method : String, path, headers = nil : HTTP::Headers?, body = nil : String | IO | Nil) : HTTP::Client::Response
     exec new_request method, path, headers, body
   end
 
@@ -361,7 +361,7 @@ class HTTP::Client
   #   response.body_io.gets # => "..."
   # end
   # ```
-  def exec(method : String, path, headers = nil : HTTP::Headers?, body = nil : String?)
+  def exec(method : String, path, headers = nil : HTTP::Headers?, body = nil : String | IO | Nil)
     exec(new_request(method, path, headers, body)) do |response|
       yield response
     end
@@ -374,7 +374,7 @@ class HTTP::Client
   # response = HTTP::Client.exec "GET", "http://www.example.com"
   # response.body # => "..."
   # ```
-  def self.exec(method, url : String | URI, headers = nil : HTTP::Headers?, body = nil : String?) : HTTP::Client::Response
+  def self.exec(method, url : String | URI, headers = nil : HTTP::Headers?, body = nil : String | IO | Nil) : HTTP::Client::Response
     exec(url) do |client, path|
       client.exec method, path, headers, body
     end
@@ -388,7 +388,7 @@ class HTTP::Client
   #   response.body_io.gets # => "..."
   # end
   # ```
-  def self.exec(method, url : String | URI, headers = nil : HTTP::Headers?, body = nil : String?)
+  def self.exec(method, url : String | URI, headers = nil : HTTP::Headers?, body = nil : String | IO | Nil)
     exec(url) do |client, path|
       client.exec(method, path, headers, body) do |response|
         yield response
diff --git a/src/http/request.cr b/src/http/request.cr
index 9684429c65d8..9b0e50367c58 100644
--- a/src/http/request.cr
+++ b/src/http/request.cr
@@ -8,12 +8,14 @@ class HTTP::Request
   getter body
   getter version
 
-  def initialize(@method : String, @resource, @headers = Headers.new : Headers, @body = nil, @version = "HTTP/1.1")
-    if body = @body
+  def initialize(@method : String, @resource, @headers = Headers.new : Headers, body = nil, @version = "HTTP/1.1")
+    if body.is_a?(String)
       @headers["Content-Length"] = body.bytesize.to_s
-    elsif @method == "POST" || @method == "PUT"
+    elsif !body && (@method == "POST" || @method == "PUT")
       @headers["Content-Length"] = "0"
     end
+
+    @body = body
   end
 
   # Returns a convenience wrapper around querying and setting cookie related
diff --git a/src/oauth/signature.cr b/src/oauth/signature.cr
index 55633c60478d..82b0b6a0894b 100644
--- a/src/oauth/signature.cr
+++ b/src/oauth/signature.cr
@@ -80,6 +80,10 @@ struct OAuth::Signature
     body = request.body
     content_type = request.headers["Content-type"]?
     if body && content_type == "application/x-www-form-urlencoded"
+      if body.is_a?(IO)
+        body = body.gets_to_end
+      end
+
       params.add_query body
     end