diff --git a/src/compile/css/Stylesheet.ts b/src/compile/css/Stylesheet.ts
index 3b1dedc4677f..882ca1c4cf45 100644
--- a/src/compile/css/Stylesheet.ts
+++ b/src/compile/css/Stylesheet.ts
@@ -2,9 +2,14 @@ import MagicString from 'magic-string';
 import { walk } from 'estree-walker';
 import Selector from './Selector';
 import Element from '../nodes/Element';
+import InlineComponent from '../nodes/InlineComponent';
 import { Node, Ast } from '../../interfaces';
 import Component from '../Component';
 
+type ClassTarget = Element
+	| InlineComponent;
+
+
 function remove_css_prefix(name: string): string {
 	return name.replace(/^-((webkit)|(moz)|(o)|(ms))-/, '');
 }
@@ -33,7 +38,7 @@ class Rule {
 		this.declarations = node.block.children.map((node: Node) => new Declaration(node));
 	}
 
-	apply(node: Element, stack: Element[]) {
+	apply(node: ClassTarget, stack: ClassTarget[]) {
 		this.selectors.forEach(selector => selector.apply(node, stack)); // TODO move the logic in here?
 	}
 
@@ -147,7 +152,7 @@ class Atrule {
 		this.children = [];
 	}
 
-	apply(node: Element, stack: Element[]) {
+	apply(node: ClassTarget, stack: ClassTarget[]) {
 		if (this.node.name === 'media' || this.node.name === 'supports') {
 			this.children.forEach(child => {
 				child.apply(node, stack);
@@ -323,10 +328,10 @@ export default class Stylesheet {
 		}
 	}
 
-	apply(node: Element) {
+	apply(node: ClassTarget) {
 		if (!this.has_styles) return;
 
-		const stack: Element[] = [];
+		const stack: ClassTarget[] = [];
 		let parent: Node = node;
 		while (parent = parent.parent) {
 			if (parent.type === 'Element') stack.unshift(parent as Element);
diff --git a/src/compile/nodes/InlineComponent.ts b/src/compile/nodes/InlineComponent.ts
index 8b6cd7728262..643a675737a6 100644
--- a/src/compile/nodes/InlineComponent.ts
+++ b/src/compile/nodes/InlineComponent.ts
@@ -1,5 +1,7 @@
 import Node from './shared/Node';
 import Attribute from './Attribute';
+import Class from './Class';
+import Text from './Text';
 import map_children from './shared/map_children';
 import Binding from './Binding';
 import EventHandler from './EventHandler';
@@ -15,6 +17,7 @@ export default class InlineComponent extends Node {
 	expression: Expression;
 	attributes: Attribute[] = [];
 	bindings: Binding[] = [];
+	classes: Class[] = [];
 	handlers: EventHandler[] = [];
 	lets: Let[] = [];
 	children: INode[];
@@ -60,10 +63,8 @@ export default class InlineComponent extends Node {
 					break;
 
 				case 'Class':
-					component.error(node, {
-						code: `invalid-class`,
-						message: `Classes can only be applied to DOM elements, not components`
-					});
+					this.classes.push(new Class(component, this, scope, node));
+					break;
 
 				case 'EventHandler':
 					this.handlers.push(new EventHandler(component, this, scope, node));
@@ -99,5 +100,31 @@ export default class InlineComponent extends Node {
 		}
 
 		this.children = map_children(component, this, this.scope, info.children);
+
+		component.stylesheet.apply(this);
+	}
+
+	add_css_class(class_name = this.component.stylesheet.id) {
+		const class_attribute = this.attributes.find(a => a.name === 'class');
+		if (class_attribute && !class_attribute.is_true) {
+			if (class_attribute.chunks.length === 1 && class_attribute.chunks[0].type === 'Text') {
+				(class_attribute.chunks[0] as Text).data += ` ${class_name}`;
+			} else {
+				(<Node[]>class_attribute.chunks).push(
+					new Text(this.component, this, this.scope, {
+						type: 'Text',
+						data: ` ${class_name}`
+					})
+				);
+			}
+		} else {
+			this.attributes.push(
+				new Attribute(this.component, this, this.scope, {
+					type: 'Attribute',
+					name: 'class',
+					value: [{ type: 'Text', data: class_name }]
+				})
+			);
+		}
 	}
 }
diff --git a/test/css/samples/component-class-dynamic/expected.css b/test/css/samples/component-class-dynamic/expected.css
new file mode 100644
index 000000000000..431f7041061e
--- /dev/null
+++ b/test/css/samples/component-class-dynamic/expected.css
@@ -0,0 +1 @@
+.foo.svelte-xyz{color:red}
\ No newline at end of file
diff --git a/test/css/samples/component-class-dynamic/input.svelte b/test/css/samples/component-class-dynamic/input.svelte
new file mode 100644
index 000000000000..483005f7e0cc
--- /dev/null
+++ b/test/css/samples/component-class-dynamic/input.svelte
@@ -0,0 +1,15 @@
+<script>
+	const Nested = window.Nested;
+
+	export let clazz = '';
+</script>
+
+<div class="foo">
+	<Nested class={ clazz } />
+</div>
+
+<style>
+	.foo {
+		color: red;
+	}
+</style>
diff --git a/test/css/samples/component-class-mixed-attrs/expected.css b/test/css/samples/component-class-mixed-attrs/expected.css
new file mode 100644
index 000000000000..a682a7dafdc1
--- /dev/null
+++ b/test/css/samples/component-class-mixed-attrs/expected.css
@@ -0,0 +1 @@
+.custom-class.svelte-xyz{color:red}
\ No newline at end of file
diff --git a/test/css/samples/component-class-mixed-attrs/input.svelte b/test/css/samples/component-class-mixed-attrs/input.svelte
new file mode 100644
index 000000000000..6902ac4a8e6e
--- /dev/null
+++ b/test/css/samples/component-class-mixed-attrs/input.svelte
@@ -0,0 +1,13 @@
+<script>
+	const Nested = window.Nested;
+
+	export let prop;
+</script>
+
+<Nested class="custom-class" prop={ prop } />
+
+<style>
+	.custom-class {
+		color: red;
+	}
+</style>
diff --git a/test/css/samples/component-class-no-definition/expected.css b/test/css/samples/component-class-no-definition/expected.css
new file mode 100644
index 000000000000..431f7041061e
--- /dev/null
+++ b/test/css/samples/component-class-no-definition/expected.css
@@ -0,0 +1 @@
+.foo.svelte-xyz{color:red}
\ No newline at end of file
diff --git a/test/css/samples/component-class-no-definition/input.svelte b/test/css/samples/component-class-no-definition/input.svelte
new file mode 100644
index 000000000000..8b0b54d7c7b5
--- /dev/null
+++ b/test/css/samples/component-class-no-definition/input.svelte
@@ -0,0 +1,13 @@
+<script>
+	const Nested = window.Nested;
+</script>
+
+<div class="foo">
+	<Nested class="no-definition" />
+</div>
+
+<style>
+	.foo {
+		color: red;
+	}
+</style>
diff --git a/test/css/samples/component-class-unused-selector/_config.js b/test/css/samples/component-class-unused-selector/_config.js
new file mode 100644
index 000000000000..f5eca632469d
--- /dev/null
+++ b/test/css/samples/component-class-unused-selector/_config.js
@@ -0,0 +1,25 @@
+export default {
+	warnings: [{
+		filename: "SvelteComponent.svelte",
+		code: `css-unused-selector`,
+		message: "Unused CSS selector",
+		start: {
+			line: 12,
+			column: 1,
+			character: 110
+		},
+		end: {
+			line: 12,
+			column: 5,
+			character: 114
+		},
+		pos: 110,
+		frame: `
+			10:   }
+			11:
+			12:   .bar {
+			      ^
+			13:     color: blue;
+			14:   }`
+	}]
+};
diff --git a/test/css/samples/component-class-unused-selector/expected.css b/test/css/samples/component-class-unused-selector/expected.css
new file mode 100644
index 000000000000..431f7041061e
--- /dev/null
+++ b/test/css/samples/component-class-unused-selector/expected.css
@@ -0,0 +1 @@
+.foo.svelte-xyz{color:red}
\ No newline at end of file
diff --git a/test/css/samples/component-class-unused-selector/input.svelte b/test/css/samples/component-class-unused-selector/input.svelte
new file mode 100644
index 000000000000..e893292c22da
--- /dev/null
+++ b/test/css/samples/component-class-unused-selector/input.svelte
@@ -0,0 +1,15 @@
+<script>
+	const Nested = window.Nested;
+</script>
+
+<Nested class="foo" />
+
+<style>
+	.foo {
+		color: red;
+	}
+
+	.bar {
+		color: blue;
+	}
+</style>
diff --git a/test/css/samples/component-class/expected.css b/test/css/samples/component-class/expected.css
new file mode 100644
index 000000000000..a682a7dafdc1
--- /dev/null
+++ b/test/css/samples/component-class/expected.css
@@ -0,0 +1 @@
+.custom-class.svelte-xyz{color:red}
\ No newline at end of file
diff --git a/test/css/samples/component-class/input.svelte b/test/css/samples/component-class/input.svelte
new file mode 100644
index 000000000000..c2479b97f1f3
--- /dev/null
+++ b/test/css/samples/component-class/input.svelte
@@ -0,0 +1,11 @@
+<script>
+	const Nested = window.Nested;
+</script>
+
+<Nested class="custom-class" />
+
+<style>
+	.custom-class {
+		color: red;
+	}
+</style>
diff --git a/test/css/samples/component-classes/expected.css b/test/css/samples/component-classes/expected.css
new file mode 100644
index 000000000000..d696774412d5
--- /dev/null
+++ b/test/css/samples/component-classes/expected.css
@@ -0,0 +1 @@
+.custom.svelte-xyz{color:red}.custom2.svelte-xyz{background:yellow}
\ No newline at end of file
diff --git a/test/css/samples/component-classes/input.svelte b/test/css/samples/component-classes/input.svelte
new file mode 100644
index 000000000000..95a35996da05
--- /dev/null
+++ b/test/css/samples/component-classes/input.svelte
@@ -0,0 +1,17 @@
+<script>
+	const Nested = window.Nested;
+
+	export let clazz = 'foo';
+</script>
+
+<Nested class="custom { clazz } custom2" />
+
+<style>
+	.custom {
+		color: red;
+	}
+
+	.custom2 {
+		background: yellow;
+	}
+</style>
diff --git a/test/js/samples/component-class-mixed-attrs/expected.js b/test/js/samples/component-class-mixed-attrs/expected.js
new file mode 100644
index 000000000000..999ec02cf6f1
--- /dev/null
+++ b/test/js/samples/component-class-mixed-attrs/expected.js
@@ -0,0 +1,61 @@
+/* generated by Svelte vX.Y.Z */
+import {
+	SvelteComponent,
+	init,
+	mount_component,
+	noop,
+	safe_not_equal
+} from "svelte/internal";
+
+function create_fragment(ctx) {
+	var current;
+
+	var nested = new ctx.Nested({ props: { class: "custom" } });
+	nested.$on("click", ctx.handleClick);
+
+	return {
+		c() {
+			nested.$$.fragment.c();
+		},
+
+		m(target, anchor) {
+			mount_component(nested, target, anchor);
+			current = true;
+		},
+
+		p: noop,
+
+		i(local) {
+			if (current) return;
+			nested.$$.fragment.i(local);
+
+			current = true;
+		},
+
+		o(local) {
+			nested.$$.fragment.o(local);
+			current = false;
+		},
+
+		d(detaching) {
+			nested.$destroy(detaching);
+		}
+	};
+}
+
+function instance($$self) {
+	const Nested = window.Nested;
+
+	let handleClick = () => {};
+
+	return { Nested, handleClick };
+}
+
+class Component extends SvelteComponent {
+	constructor(options) {
+		super();
+		init(this, options, instance, create_fragment, safe_not_equal, []);
+	}
+}
+
+export default Component;
diff --git a/test/js/samples/component-class-mixed-attrs/input.svelte b/test/js/samples/component-class-mixed-attrs/input.svelte
new file mode 100644
index 000000000000..50b335a7d385
--- /dev/null
+++ b/test/js/samples/component-class-mixed-attrs/input.svelte
@@ -0,0 +1,7 @@
+<script>
+	const Nested = window.Nested;
+
+	let handleClick = () => {};
+</script>
+
+<Nested class="custom" on:click={ handleClick } />
diff --git a/test/js/samples/component-class-no-definition/expected.js b/test/js/samples/component-class-no-definition/expected.js
new file mode 100644
index 000000000000..e4913283632e
--- /dev/null
+++ b/test/js/samples/component-class-no-definition/expected.js
@@ -0,0 +1,77 @@
+/* generated by Svelte vX.Y.Z */
+import {
+	SvelteComponent,
+	append,
+	detach,
+	element,
+	init,
+	insert,
+	mount_component,
+	noop,
+	safe_not_equal
+} from "svelte/internal";
+
+function add_css() {
+	var style = element("style");
+	style.id = 'svelte-sg04hs-style';
+	style.textContent = ".foo.svelte-sg04hs{color:red}";
+	append(document.head, style);
+}
+
+function create_fragment(ctx) {
+	var div, current;
+
+	var nested = new ctx.Nested({ props: { class: "no-definition" } });
+
+	return {
+		c() {
+			div = element("div");
+			nested.$$.fragment.c();
+			div.className = "foo svelte-sg04hs";
+		},
+
+		m(target, anchor) {
+			insert(target, div, anchor);
+			mount_component(nested, div, null);
+			current = true;
+		},
+
+		p: noop,
+
+		i(local) {
+			if (current) return;
+			nested.$$.fragment.i(local);
+
+			current = true;
+		},
+
+		o(local) {
+			nested.$$.fragment.o(local);
+			current = false;
+		},
+
+		d(detaching) {
+			if (detaching) {
+				detach(div);
+			}
+
+			nested.$destroy();
+		}
+	};
+}
+
+function instance($$self) {
+	const Nested = window.Nested;
+
+	return { Nested };
+}
+
+class Component extends SvelteComponent {
+	constructor(options) {
+		super();
+		if (!document.getElementById("svelte-sg04hs-style")) add_css();
+		init(this, options, instance, create_fragment, safe_not_equal, []);
+	}
+}
+
+export default Component;
diff --git a/test/js/samples/component-class-no-definition/input.svelte b/test/js/samples/component-class-no-definition/input.svelte
new file mode 100644
index 000000000000..8b0b54d7c7b5
--- /dev/null
+++ b/test/js/samples/component-class-no-definition/input.svelte
@@ -0,0 +1,13 @@
+<script>
+	const Nested = window.Nested;
+</script>
+
+<div class="foo">
+	<Nested class="no-definition" />
+</div>
+
+<style>
+	.foo {
+		color: red;
+	}
+</style>
diff --git a/test/js/samples/component-class/expected.js b/test/js/samples/component-class/expected.js
new file mode 100644
index 000000000000..0f92a9c6a13b
--- /dev/null
+++ b/test/js/samples/component-class/expected.js
@@ -0,0 +1,70 @@
+/* generated by Svelte vX.Y.Z */
+import {
+	SvelteComponent,
+	append,
+	element,
+	init,
+	mount_component,
+	noop,
+	safe_not_equal
+} from "svelte/internal";
+
+function add_css() {
+	var style = element("style");
+	style.id = 'svelte-1rk2jaa-style';
+	style.textContent = ".custom.svelte-1rk2jaa{color:'blue'}";
+	append(document.head, style);
+}
+
+function create_fragment(ctx) {
+	var current;
+
+	var nested = new ctx.Nested({
+		props: { class: "custom svelte-1rk2jaa" }
+	});
+
+	return {
+		c() {
+			nested.$$.fragment.c();
+		},
+
+		m(target, anchor) {
+			mount_component(nested, target, anchor);
+			current = true;
+		},
+
+		p: noop,
+
+		i(local) {
+			if (current) return;
+			nested.$$.fragment.i(local);
+
+			current = true;
+		},
+
+		o(local) {
+			nested.$$.fragment.o(local);
+			current = false;
+		},
+
+		d(detaching) {
+			nested.$destroy(detaching);
+		}
+	};
+}
+
+function instance($$self) {
+	const Nested = window.Nested;
+
+	return { Nested };
+}
+
+class Component extends SvelteComponent {
+	constructor(options) {
+		super();
+		if (!document.getElementById("svelte-1rk2jaa-style")) add_css();
+		init(this, options, instance, create_fragment, safe_not_equal, []);
+	}
+}
+
+export default Component;
diff --git a/test/js/samples/component-class/input.svelte b/test/js/samples/component-class/input.svelte
new file mode 100644
index 000000000000..9520bcf9055f
--- /dev/null
+++ b/test/js/samples/component-class/input.svelte
@@ -0,0 +1,11 @@
+<script>
+	const Nested = window.Nested;
+</script>
+
+<Nested class="custom" />
+
+<style>
+	.custom {
+		color: 'blue';
+	}
+</style>
diff --git a/test/js/samples/component-classes/expected.js b/test/js/samples/component-classes/expected.js
new file mode 100644
index 000000000000..ebf0b40e78c3
--- /dev/null
+++ b/test/js/samples/component-classes/expected.js
@@ -0,0 +1,77 @@
+/* generated by Svelte vX.Y.Z */
+import {
+	SvelteComponent,
+	append,
+	element,
+	init,
+	mount_component,
+	safe_not_equal
+} from "svelte/internal";
+
+function add_css() {
+	var style = element("style");
+	style.id = 'svelte-167wvy9-style';
+	style.textContent = ".custom.svelte-167wvy9{color:'blue'}.custom2.svelte-167wvy9{background:'fuchsia'}";
+	append(document.head, style);
+}
+
+function create_fragment(ctx) {
+	var current;
+
+	var nested = new ctx.Nested({
+		props: {
+		class: "custom custom2 " + otherCls + " svelte-167wvy9"
+	}
+	});
+
+	return {
+		c() {
+			nested.$$.fragment.c();
+		},
+
+		m(target, anchor) {
+			mount_component(nested, target, anchor);
+			current = true;
+		},
+
+		p(changed, ctx) {
+			var nested_changes = {};
+			if (changed.otherCls) nested_changes.class = "custom custom2 " + otherCls + " svelte-167wvy9";
+			nested.$set(nested_changes);
+		},
+
+		i(local) {
+			if (current) return;
+			nested.$$.fragment.i(local);
+
+			current = true;
+		},
+
+		o(local) {
+			nested.$$.fragment.o(local);
+			current = false;
+		},
+
+		d(detaching) {
+			nested.$destroy(detaching);
+		}
+	};
+}
+
+let otherCls = 'asd';
+
+function instance($$self) {
+	const Nested = window.Nested;
+
+	return { Nested };
+}
+
+class Component extends SvelteComponent {
+	constructor(options) {
+		super();
+		if (!document.getElementById("svelte-167wvy9-style")) add_css();
+		init(this, options, instance, create_fragment, safe_not_equal, []);
+	}
+}
+
+export default Component;
diff --git a/test/js/samples/component-classes/input.svelte b/test/js/samples/component-classes/input.svelte
new file mode 100644
index 000000000000..319bda9b1597
--- /dev/null
+++ b/test/js/samples/component-classes/input.svelte
@@ -0,0 +1,17 @@
+<script>
+	const Nested = window.Nested;
+
+	let otherCls = 'asd';
+</script>
+
+<Nested class="custom custom2 {otherCls}" />
+
+<style>
+	.custom {
+		color: 'blue';
+	}
+
+	.custom2 {
+		background: 'fuchsia';
+	}
+</style>
diff --git a/test/server-side-rendering/samples/component-class/Widget.svelte b/test/server-side-rendering/samples/component-class/Widget.svelte
new file mode 100644
index 000000000000..824f45d03382
--- /dev/null
+++ b/test/server-side-rendering/samples/component-class/Widget.svelte
@@ -0,0 +1,7 @@
+<script>
+  let clazz;
+
+  export { clazz as class };
+</script>
+
+<p class={ clazz }>i am a widget</p>
diff --git a/test/server-side-rendering/samples/component-class/_expected.css b/test/server-side-rendering/samples/component-class/_expected.css
new file mode 100644
index 000000000000..b087f254067c
--- /dev/null
+++ b/test/server-side-rendering/samples/component-class/_expected.css
@@ -0,0 +1 @@
+.foo.svelte-40y5y5{color:yellow}
\ No newline at end of file
diff --git a/test/server-side-rendering/samples/component-class/_expected.html b/test/server-side-rendering/samples/component-class/_expected.html
new file mode 100644
index 000000000000..9a6eea662d08
--- /dev/null
+++ b/test/server-side-rendering/samples/component-class/_expected.html
@@ -0,0 +1 @@
+<div><p class="foo svelte-40y5y5">i am a widget</p></div>
diff --git a/test/server-side-rendering/samples/component-class/main.svelte b/test/server-side-rendering/samples/component-class/main.svelte
new file mode 100644
index 000000000000..b458f349af8c
--- /dev/null
+++ b/test/server-side-rendering/samples/component-class/main.svelte
@@ -0,0 +1,13 @@
+<script>
+	import Widget from './Widget.svelte';
+</script>
+
+<style>
+	.foo {
+		color: yellow;
+	}
+</style>
+
+<div>
+	<Widget class="foo" />
+</div>