diff --git a/lib/protocol/http/header/cookie.rb b/lib/protocol/http/header/cookie.rb
index f86c97f..427f701 100644
--- a/lib/protocol/http/header/cookie.rb
+++ b/lib/protocol/http/header/cookie.rb
@@ -12,7 +12,40 @@ module Header
 			# The `cookie` header contains stored HTTP cookies previously sent by the server with the `set-cookie` header.
 			#
 			# It is used by clients to send key-value pairs representing stored cookies back to the server.
-			class Cookie < Multiple
+			# Multiple cookies within a single `Cookie` header are joined with `"; "` per RFC 6265.
+			class Cookie < Array
+				# Parses a raw header value.
+				#
+				# @parameter value [String] a single raw header value.
+				# @returns [Cookie] a new instance containing the parsed value.
+				def self.parse(value)
+					self.new([value])
+				end
+
+				# Coerces a value into a parsed header object.
+				#
+				# @parameter value [String | Array] the value to coerce.
+				# @returns [Cookie] a parsed header object.
+				def self.coerce(value)
+					case value
+					when Array
+						self.new(value.map(&:to_s))
+					else
+						self.parse(value.to_s)
+					end
+				end
+
+				# Initializes the cookie header with the given values.
+				#
+				# @parameter value [Array | Nil] an array of cookie strings, or `nil` for an empty header.
+				def initialize(value = nil)
+					super()
+
+					if value
+						self.concat(value)
+					end
+				end
+
 				# Parses the `cookie` header into a hash of cookie names and their corresponding cookie objects.
 				#
 				# @returns [Hash(String, HTTP::Cookie)] a hash where keys are cookie names and values are {HTTP::Cookie} objects.
@@ -20,15 +53,15 @@ def to_h
 					cookies = self.collect do |string|
 						HTTP::Cookie.parse(string)
 					end
-					
+
 					cookies.map{|cookie| [cookie.name, cookie]}.to_h
 				end
-				
-				# Serializes the `cookie` header by joining individual cookie strings with semicolons.
+
+				# Serializes the `cookie` header by joining individual cookie strings with `"; "` per RFC 6265.
 				def to_s
-					join(";")
+					join("; ")
 				end
-				
+
 				# Whether this header is acceptable in HTTP trailers.
 				# Cookie headers should not appear in trailers as they contain state information needed early in processing.
 				# @returns [Boolean] `false`, as cookie headers are needed during initial request processing.
@@ -36,11 +69,29 @@ def self.trailer?
 					false
 				end
 			end
-			
+
 			# The `set-cookie` header sends cookies from the server to the user agent.
 			#
-			# It is used to store cookies on the client side, which are then sent back to the server in subsequent requests using the `cookie` header.
-			class SetCookie < Cookie
+			# Each `Set-Cookie` header must be a separate header field — they cannot be combined.
+			# It is used to store cookies on the client side, which are then sent back to the server
+			# in subsequent requests using the `cookie` header.
+			class SetCookie < Multiple
+				# Parses the `set-cookie` headers into a hash of cookie names and their corresponding cookie objects.
+				#
+				# @returns [Hash(String, HTTP::Cookie)] a hash where keys are cookie names and values are {HTTP::Cookie} objects.
+				def to_h
+					cookies = self.collect do |string|
+						HTTP::Cookie.parse(string)
+					end
+
+					cookies.map{|cookie| [cookie.name, cookie]}.to_h
+				end
+
+				# Whether this header is acceptable in HTTP trailers.
+				# @returns [Boolean] `false`, as set-cookie headers are needed during initial response processing.
+				def self.trailer?
+					false
+				end
 			end
 		end
 	end
diff --git a/lib/protocol/http/headers.rb b/lib/protocol/http/headers.rb
index 76dcb5a..bc00ac9 100644
--- a/lib/protocol/http/headers.rb
+++ b/lib/protocol/http/headers.rb
@@ -299,8 +299,14 @@ def []=(key, value)
 				if @indexed
 					@indexed[key] = value
 				end
-				
-				@fields << [key, value.to_s]
+
+				if value.is_a?(Multiple)
+					value.each do |v|
+						@fields << [key, v.to_s]
+					end
+				else
+					@fields << [key, value.to_s]
+				end
 			end
 			
 			# Get the value of the specified header key.
diff --git a/test/protocol/http/header/cookie.rb b/test/protocol/http/header/cookie.rb
index 7b108dc..a866ffa 100644
--- a/test/protocol/http/header/cookie.rb
+++ b/test/protocol/http/header/cookie.rb
@@ -56,8 +56,8 @@
 			cookie
 		end
 		
-		it "joins cookies with semicolons without spaces" do
-			expect(header.to_s).to be == "session=abc123;user_id=42;token=xyz789"
+		it "joins cookies with semicolons and spaces per RFC 6265" do
+			expect(header.to_s).to be == "session=abc123; user_id=42; token=xyz789"
 		end
 	end
 end
diff --git a/test/protocol/http/headers.rb b/test/protocol/http/headers.rb
index e5bb9b2..69de97b 100644
--- a/test/protocol/http/headers.rb
+++ b/test/protocol/http/headers.rb
@@ -600,7 +600,7 @@ def self.trailer?
 	
 	with "set-cookie" do
 		it "can extract parsed cookies" do
-			expect(headers["set-cookie"]).to be_a(Protocol::HTTP::Header::Cookie)
+			expect(headers["set-cookie"]).to be_a(Protocol::HTTP::Header::SetCookie)
 		end
 	end