diff --git a/lib/protocol/url/reference.rb b/lib/protocol/url/reference.rb
index b8f94b4..b0dbee6 100644
--- a/lib/protocol/url/reference.rb
+++ b/lib/protocol/url/reference.rb
@@ -132,6 +132,8 @@ def parameters?
 			#
 			# Afterwards, the `query` attribute will be cleared.
 			#
+			# If there is no query string or existing parameters, an empty mutable hash is created.
+			#
 			# @returns [Hash] The merged parameters.
 			def parse_query!(encoding = Encoding)
 				if @query and !@query.empty?
@@ -146,7 +148,7 @@ def parse_query!(encoding = Encoding)
 					@query = nil
 				end
 				
-				return @parameters
+				return @parameters ||= {}
 			end
 			
 			# @returns [Boolean] Whether the reference has a query string.
diff --git a/test/protocol/url/reference.rb b/test/protocol/url/reference.rb
index 7ec71af..9370b41 100644
--- a/test/protocol/url/reference.rb
+++ b/test/protocol/url/reference.rb
@@ -598,6 +598,16 @@
 			expect(reference.parameters).to be == {"foo" => "bar"}
 		end
 		
+		it "creates mutable parameters when there is no query string" do
+			reference = subject.parse("/path")
+			
+			parameters = reference.parse_query!
+			parameters["foo"] = "bar"
+			
+			expect(reference.parameters).to be == {"foo" => "bar"}
+			expect(reference.to_s).to be == "/path?foo=bar"
+		end
+		
 		it "updates to_s output after parsing" do
 			reference = subject.parse("/path?foo=bar&baz=qux")
 			expect(reference.to_s).to be == "/path?foo=bar&baz=qux"