diff --git a/lib/utopia/session/lazy_hash.rb b/lib/utopia/session/lazy_hash.rb
index e28d7497..f4c90887 100644
--- a/lib/utopia/session/lazy_hash.rb
+++ b/lib/utopia/session/lazy_hash.rb
@@ -16,10 +16,6 @@ def initialize(&block)
 				@loader = block
 			end
 			
-			# The loaded session values, if already loaded.
-			# @returns [Hash | Nil] The loaded values.
-			attr :values
-			
 			# Fetch a value by key, loading the hash if necessary.
 			# @parameter key [Object] The key.
 			# @returns [Object | Nil] The value.
@@ -66,10 +62,20 @@ def changed?
 				@changed
 			end
 			
-			# Load and return the underlying values.
-			# @returns [Hash] The loaded values.
-			def load!
-				@values ||= @loader.call
+			# Persist the session values if they have changed or require updating.
+			# @parameter timeout [Numeric | Nil] The maximum age before an update is required.
+			# @yields {|values, updated_at| ...} The loaded values and their update time.
+			# @returns [Object | Nil] The result of the block if persistence was required.
+			def persist(timeout = nil)
+				return unless needs_update?(timeout)
+				
+				values = load!
+				updated_at = values[:updated_at] = Time.now.utc
+				
+				result = yield(values, updated_at)
+				@changed = false
+				
+				return result
 			end
 			
 			# Check whether the underlying values have been loaded.
@@ -93,6 +99,13 @@ def needs_update?(timeout = nil)
 				
 				return false
 			end
+			
+			private
+			
+			# Load and return the underlying values.
+			def load!
+				@values ||= @loader.call
+			end
 		end
 	end
 end
diff --git a/lib/utopia/session/middleware.rb b/lib/utopia/session/middleware.rb
index 90819fa6..d5be1110 100644
--- a/lib/utopia/session/middleware.rb
+++ b/lib/utopia/session/middleware.rb
@@ -149,14 +149,8 @@ def prepare_session(request)
 			end
 			
 			def update_session(session_hash, headers)
-				if session_hash.needs_update?(@update_timeout)
-					values = session_hash.values
-					
-					values[:updated_at] = Time.now.utc
-					
-					data = encrypt(session_hash.values)
-					
-					commit(data, values[:updated_at], headers)
+				session_hash.persist(@update_timeout) do |values, updated_at|
+					commit(encrypt(values), updated_at, headers)
 				end
 			end
 			
diff --git a/test/utopia/session.rb b/test/utopia/session.rb
index b353cd6b..449f9c65 100755
--- a/test/utopia/session.rb
+++ b/test/utopia/session.rb
@@ -399,4 +399,42 @@ def before
 		
 		expect(hash).to be(:needs_update?)
 	end
+	
+	it "should persist changed values" do
+		hash = Utopia::Session::LazyHash.new do
+			{a: 10}
+		end
+		
+		hash[:a] = 20
+		persisted_at = Time.now.utc
+		
+		result = hash.persist do |values, updated_at|
+			expect(values[:a]).to be == 20
+			expect(updated_at).to be >= persisted_at
+			expect(values[:updated_at]).to be_equal(updated_at)
+			
+			:complete
+		end
+		
+		expect(result).to be == :complete
+		expect(hash).not.to be(:changed?)
+		expect(hash).not.to be(:respond_to?, :values)
+		expect(hash).not.to be(:respond_to?, :load!)
+	end
+	
+	it "should retain changes if persistence fails" do
+		hash = Utopia::Session::LazyHash.new do
+			{a: 10}
+		end
+		
+		hash[:a] = 20
+		
+		expect do
+			hash.persist do
+				raise "Persistence failed!"
+			end
+		end.to raise_exception(RuntimeError, message: be == "Persistence failed!")
+		
+		expect(hash).to be(:changed?)
+	end
 end