diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0746730f..f6865659 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 * Fix setting `value` not working server-side on `<textarea>` elements
 * Add `Renderer#handleError()` method
 * Newlines are no longer an expression delimiter, only semicolons are
+* Fix `Renderer#addSubtemplate(template, variables)` not preparing variables properly
 
 ## 2.3.15 (2023-11-27)
 
diff --git a/lib/core/renderer.js b/lib/core/renderer.js
index c1f74bee..4faacf44 100644
--- a/lib/core/renderer.js
+++ b/lib/core/renderer.js
@@ -3036,7 +3036,7 @@ Renderer.setCommand(function bottom() {
  *
  * @author   Jelle De Loecker   <jelle@elevenways.be>
  * @since    1.0.0
- * @version  2.3.7
+ * @version  2.3.16
  *
  * @param    {Array|String}  names       The partial to render
  * @param    {Object}        options
@@ -3067,10 +3067,14 @@ Renderer.setMethod(function addSubtemplate(names, options, variables) {
 	templates.is_subtemplate = true;
 
 	// Get the current element
-	variables.$ancestor_element = this.$0;
+	const ancestor_element = this.$0;
 
 	placeholder = this.async(function renderSubtemplate(next) {
 
+		// The Templates render method expects fully prepared variables.
+		variables = this.prepareVariables(variables);
+		variables.$ancestor_element = ancestor_element;
+
 		templates.render(variables).done(function done(err, block) {
 
 			if (err) {
diff --git a/lib/element/html_element_extensions.js b/lib/element/html_element_extensions.js
index 12df03db..f09d788f 100644
--- a/lib/element/html_element_extensions.js
+++ b/lib/element/html_element_extensions.js
@@ -224,7 +224,8 @@ Blast.definePrototype(Element, 'incrementIndexInParent', function incrementIndex
  */
 Blast.definePrototype(Element, 'transferStylesTo', function transferStylesTo(target, properties) {
 
-	var styles = window.getComputedStyle(this),
+	let styles = window.getComputedStyle(this),
+	    key,
 	    i;
 
 	if (!properties) {
@@ -285,13 +286,11 @@ Blast.definePrototype(Element, 'isFocusable', function isFocusable() {
  */
 Blast.definePrototype(Element, 'isTabbable', function isTabbable() {
 
-	var tabindex;
-
 	if (!ProtoEl.isFocusable.call(this)) {
 		return false;
 	}
 
-	tabindex = this.getAttribute('tabindex');
+	let tabindex = this.getAttribute('tabindex');
 
 	if (tabindex && tabindex[0] == '-') {
 		return false;
diff --git a/test/30-renderer.js b/test/30-renderer.js
index 7d53e821..f26fc834 100644
--- a/test/30-renderer.js
+++ b/test/30-renderer.js
@@ -2,6 +2,19 @@ var assert   = require('assert'),
     Hawkejs  = require('../index.js'),
     hawkejs;
 
+const Blast = __Protoblast;
+
+const RENDER = (done, ...render_args) => {
+	let callback = render_args.pop();
+	return hawkejs.render(...render_args, (...args) => {
+		try {
+			callback(...args);
+		} catch (err) {
+			done(err);
+		}
+	});
+}
+
 describe('Renderer', function() {
 
 	before(function() {
@@ -23,7 +36,7 @@ describe('Renderer', function() {
 
 			var compiled = hawkejs.compile('async_test_1', code);
 
-			hawkejs.render(compiled, {}, function rendered(err, res) {
+			RENDER(done, compiled, {}, function rendered(err, res) {
 
 				if (err) {
 					throw err;
@@ -40,7 +53,7 @@ describe('Renderer', function() {
 	describe('#assign(name)', function() {
 		it('sets the wanted block content', function(done) {
 
-			hawkejs.render('assign_test', function doneAssignTest(err, result) {
+			RENDER(done, 'assign_test', function doneAssignTest(err, result) {
 
 				if (err) {
 					throw err;
@@ -59,7 +72,7 @@ This is the internally set main
 
 	describe('#assign_end()', function() {
 		it('should claim the siblings', function(done) {
-			hawkejs.render('assign_end', function doneAssignTest(err, result) {
+			RENDER(done, 'assign_end', function doneAssignTest(err, result) {
 
 				if (err) {
 					throw err;
@@ -74,7 +87,7 @@ This is the internally set main
 
 	describe('#expands(template)', function() {
 		it('expands into the given template', function(done) {
-			hawkejs.render('expand_test', function doneExpandTest(err, result) {
+			RENDER(done, 'expand_test', function doneExpandTest(err, result) {
 
 				if (err) {
 					throw err;
@@ -93,7 +106,7 @@ This is the main content
 
 		it('should be possible to use the {% extend %} expression instead', function(done) {
 
-			hawkejs.render('extend_test', function doneExpandTest(err, result) {
+			RENDER(done, 'extend_test', function doneExpandTest(err, result) {
 
 				if (err) {
 					throw err;
@@ -115,7 +128,7 @@ This is the main content
 	describe('#start(name, options)', function() {
 		it('should add block classes if given', function(done) {
 
-			hawkejs.render('assign_test_class', function doneExpandTest(err, result) {
+			RENDER(done, 'assign_test_class', function doneExpandTest(err, result) {
 
 				if (err) {
 					throw err;
@@ -128,9 +141,50 @@ This is the main content
 		});
 	});
 
+	describe('#addSubTemplate(template, options)', () => {
+		it('should correctly convert the variables', (done) => {
+
+			let CloneTestClass = Blast.Collection.Function.inherits(null, function CloneTestClass(value) {
+				this.value = value;
+			});
+
+			CloneTestClass.setMethod(function toHawkejs() {
+				return new CloneTestClass(this.value + '!!!');
+			});
+
+			let value = new CloneTestClass('test');
+
+			let renderer = hawkejs.createRenderer();
+			renderer.set('test_instance', value);
+
+			let source = `The value is: "<%= test_instance.value %>"`;
+
+			let compiled = hawkejs.compile(source);
+			let placeholder = renderer.addSubtemplate(compiled, {print: false});
+
+			//let cloned = Blast.Bound.JSON.clone(value, 'toHawkejs')
+
+			placeholder.getContent(function gotContent(err, block_buffer) {
+
+				if (err) {
+					return done(err);
+				}
+
+				try {
+					assert.strictEqual(block_buffer.toHTML(), 'The value is: "test!!!"');
+				} catch (err) {
+					return done(err);
+				}
+
+				done();
+			});
+
+		});
+	});
+
 	describe('#implement(name)', function() {
 		it('should print the given element', function(done) {
-			hawkejs.render('implement_test', function doneImplement(err, result) {
+			RENDER(done, 'implement_test', function doneImplement(err, result) {
 
 				if (err) {
 					throw err;
@@ -142,7 +196,7 @@ This is the main content
 		});
 
 		it('should include assignments', function(done) {
-			hawkejs.render('implement_blocks', function doneImplement(err, result) {
+			RENDER(done, 'implement_blocks', function doneImplement(err, result) {
 
 				if (err) {
 					throw err;
@@ -157,7 +211,7 @@ This is the main content
 		});
 
 		it('should work on assignments', function(done) {
-			hawkejs.render('expand_start_implement_assign', function doneImplement(err, result) {
+			RENDER(done, 'expand_start_implement_assign', function doneImplement(err, result) {
 
 				if (err) {
 					throw err;
@@ -175,7 +229,7 @@ This is the main content
 
 	describe('#include(name)', function() {
 		it('should only be executed if in a used block', function(done) {
-			hawkejs.render('expand_start_include_assign', function doneImplement(err, result) {
+			RENDER(done, 'expand_start_include_assign', function doneImplement(err, result) {
 
 				if (err) {
 					throw err;
@@ -192,7 +246,7 @@ This is the main content
 
 		it('should set the correct ancestor element', function(done) {
 
-			hawkejs.render('include_parent_test', function doneImplement(err, result) {
+			RENDER(done, 'include_parent_test', function doneImplement(err, result) {
 
 				if (err) {
 					throw err;
@@ -213,7 +267,7 @@ This is the main content
 				count : 0,
 			};
 
-			hawkejs.render('include_with_variables', root_variables, function doneImplement(err, result) {
+			RENDER(done, 'include_with_variables', root_variables, function doneImplement(err, result) {
 
 				if (err) {
 					throw err;
@@ -255,7 +309,7 @@ This is the main content
 
 	describe('#partial(name)', function() {
 		it('should render a partial in a new scope', function(done) {
-			hawkejs.render('print_partial', function donePartial(err, result) {
+			RENDER(done, 'print_partial', function donePartial(err, result) {
 
 				if (err) {
 					throw err;
@@ -277,7 +331,7 @@ This is the main content
 		});
 
 		it('should allow using scoped blocks with implements', function(done) {
-			hawkejs.render('partial_with_implements', function donePartial(err, result) {
+			RENDER(done, 'partial_with_implements', function donePartial(err, result) {
 
 				if (err) {
 					throw err;
@@ -293,7 +347,7 @@ This is the main content
 
 	describe('Template#switchTemplate(name, variables)', function() {
 		it('should allow using scoped blocks that switch target blocks', function(done) {
-			hawkejs.render('partial_with_switch_template', function donePartial(err, result) {
+			RENDER(done, 'partial_with_switch_template', function donePartial(err, result) {
 
 				if (err) {
 					throw err;
@@ -307,7 +361,7 @@ This is the main content
 		});
 
 		it('should allow switching to another template in the start template', function(done) {
-			hawkejs.render('partial_with_root_switch_and_implement', function donePartial(err, result) {
+			RENDER(done, 'partial_with_root_switch_and_implement', function donePartial(err, result) {
 
 				if (err) {
 					throw err;
@@ -322,7 +376,7 @@ This is the main content
 	describe('#foundation()', function() {
 		it('should not wait for placeholders that are waiting for itself', function(done) {
 
-			let renderer = hawkejs.render('implement_with_foundation_extension', function doneImplement(err, result) {
+			let renderer = RENDER(done, 'implement_with_foundation_extension', function doneImplement(err, result) {
 
 				if (err) {
 					return done(err);
@@ -356,7 +410,7 @@ This is the main content
 	describe('#setTheme(name)', function() {
 		it('should set the theme to use for partials', function(done) {
 
-			let renderer = hawkejs.render('implement_blocks', function doneImplement(err, result) {
+			let renderer = RENDER(done, 'implement_blocks', function doneImplement(err, result) {
 
 				if (err) {
 					throw err;
@@ -371,7 +425,7 @@ This is the main content
 
 		it('should set the theme to use for extensions', function(done) {
 
-			let renderer = hawkejs.render('expand_test', function doneImplement(err, result) {
+			let renderer = RENDER(done, 'expand_test', function doneImplement(err, result) {
 
 				if (err) {
 					throw err;
@@ -388,7 +442,7 @@ This is the main content
 	describe('#$0', function() {
 		it('is a local property that refers to the current element', function(done) {
 
-			let renderer = hawkejs.render('local_property_test', function doneTest(err, result) {
+			let renderer = RENDER(done, 'local_property_test', function doneTest(err, result) {
 
 				if (err) {
 					throw err;
@@ -412,7 +466,7 @@ This is the main content
 
 	describe('#style()', function() {
 		it('should add stylesheet elements', function(done) {
-			hawkejs.render('style_test', function doneImplement(err, result) {
+			RENDER(done, 'style_test', function doneImplement(err, result) {
 
 				if (err) {
 					throw err;