diff --git a/spec/std/http/server/server_spec.cr b/spec/std/http/server/server_spec.cr
index d345472e5a5e..296b2a200343 100644
--- a/spec/std/http/server/server_spec.cr
+++ b/spec/std/http/server/server_spec.cr
@@ -285,6 +285,66 @@ module HTTP
       HTTP::Client.get("http://#{address1}/").body.should eq "Test Server (#{address1})"
     end
 
+    it "handles Expect: 100-continue correctly when body is read" do
+      server = Server.new do |context|
+        context.response << context.request.body.not_nil!.gets_to_end
+      end
+
+      address = server.bind_unused_port
+      spawn server.listen
+
+      wait_for { server.listening? }
+
+      TCPSocket.open(address.address, address.port) do |socket|
+        socket << requestize(<<-REQUEST
+          POST / HTTP/1.1
+          Expect: 100-continue
+          Content-Length: 5
+
+          REQUEST
+        )
+        socket << "\r\n"
+        socket.flush
+
+        response = Client::Response.from_io(socket)
+        response.status_code.should eq(100)
+
+        socket << "hello"
+        socket.flush
+
+        response = Client::Response.from_io(socket)
+        response.status_code.should eq(200)
+        response.body.should eq("hello")
+      end
+    end
+
+    it "handles Expect: 100-continue correctly when body isn't read" do
+      server = Server.new do |context|
+        context.response.respond_with_error("I don't want your body", 400)
+      end
+
+      address = server.bind_unused_port
+      spawn server.listen
+
+      wait_for { server.listening? }
+
+      TCPSocket.open(address.address, address.port) do |socket|
+        socket << requestize(<<-REQUEST
+          POST / HTTP/1.1
+          Expect: 100-continue
+          Content-Length: 5
+
+          REQUEST
+        )
+        socket << "\r\n"
+        socket.flush
+
+        response = Client::Response.from_io(socket)
+        response.status_code.should eq(400)
+        response.body.should eq("400 I don't want your body\n")
+      end
+    end
+
     it "lists addresses" do
       server = Server.new { }
 
diff --git a/src/http/common.cr b/src/http/common.cr
index 1907bef8c8d5..bc6689c55592 100644
--- a/src/http/common.cr
+++ b/src/http/common.cr
@@ -27,6 +27,7 @@ module HTTP
 
       if line.empty?
         body = nil
+
         if body_type.prohibited?
           body = nil
         elsif content_length = content_length(headers)
@@ -40,6 +41,10 @@ module HTTP
           body = UnknownLengthContent.new(io)
         end
 
+        if body.is_a?(Content) && expect_continue?(headers)
+          body.expects_continue = true
+        end
+
         if decompress && body
           {% if flag?(:without_zlib) %}
             raise "Can't decompress because `-D without_zlib` was passed at compile time"
@@ -194,6 +199,10 @@ module HTTP
     end
   end
 
+  def self.expect_continue?(headers)
+    headers["Expect"]?.try(&.downcase) == "100-continue"
+  end
+
   record ComputedContentTypeHeader,
     content_type : String?,
     charset : String?
diff --git a/src/http/content.cr b/src/http/content.cr
index da5875570482..218821dc127e 100644
--- a/src/http/content.cr
+++ b/src/http/content.cr
@@ -3,16 +3,50 @@ require "http/common"
 module HTTP
   # :nodoc:
   module Content
+    CONTINUE = "HTTP/1.1 100 Continue\r\n\r\n"
+
+    @continue_sent = false
+    setter expects_continue : Bool = false
+
     def close
+      @expects_continue = false
       skip_to_end
       super
     end
+
+    protected def ensure_send_continue
+      return unless @expects_continue
+      return if @continue_sent
+      @io << CONTINUE
+      @io.flush
+      @continue_sent = true
+    end
   end
 
   # :nodoc:
   class FixedLengthContent < IO::Sized
     include Content
 
+    def read(slice : Bytes)
+      ensure_send_continue
+      super
+    end
+
+    def read_byte
+      ensure_send_continue
+      super
+    end
+
+    def peek
+      ensure_send_continue
+      super
+    end
+
+    def skip(bytes_count)
+      ensure_send_continue
+      super
+    end
+
     def write(slice : Bytes)
       raise IO::Error.new "Can't write to FixedLengthContent"
     end
@@ -26,14 +60,17 @@ module HTTP
     end
 
     def read(slice : Bytes)
+      ensure_send_continue
       @io.read(slice)
     end
 
     def read_byte
+      ensure_send_continue
       @io.read_byte
     end
 
     def peek
+      ensure_send_continue
       @io.peek
     end
 
@@ -66,6 +103,7 @@ module HTTP
     end
 
     def read(slice : Bytes)
+      ensure_send_continue
       count = slice.size
       return 0 if count == 0
 
@@ -87,6 +125,7 @@ module HTTP
     end
 
     def read_byte
+      ensure_send_continue
       next_chunk
       return super if @received_final_chunk
 
@@ -100,6 +139,7 @@ module HTTP
     end
 
     def peek
+      ensure_send_continue
       next_chunk
       return Bytes.empty if @received_final_chunk
 
@@ -115,6 +155,7 @@ module HTTP
     end
 
     def skip(bytes_count)
+      ensure_send_continue
       if bytes_count <= @chunk_remaining
         @io.skip(bytes_count)
         @chunk_remaining -= bytes_count