diff --git a/src/compiler/compile/Component.ts b/src/compiler/compile/Component.ts
index 85623c6da7..8ed8e3390d 100644
--- a/src/compiler/compile/Component.ts
+++ b/src/compiler/compile/Component.ts
@@ -788,26 +788,25 @@ export default class Component {
 					scope = map.get(node);
 				}
 
-                let deep = false;
-                let names: string[] | null;
+				let deep = false;
+				let names: string[] | null;
 
-                if (node.type === 'AssignmentExpression') {
+				if (node.type === 'AssignmentExpression') {
 						deep = node.left.type === 'MemberExpression';
 						names = deep
 							? [get_object(node.left).name]
 							: extract_names(node.left);
                 } else if (node.type === 'UpdateExpression') {
-                    deep = node.argument.type === 'MemberExpression';
-                    const { name } = get_object(node.argument);
-                    names = [name];
+					deep = node.argument.type === 'MemberExpression';
+					const { name } = get_object(node.argument);
+					names = [name];
 				}
-
 				
 				if (names) {
 					names.forEach(name => {
 						const variable = component.var_lookup.get(name);
 						if (variable && variable.writable === false && !deep) {
-							component.warn(node as any, {
+							component.error(node as any, {
 								code: 'assignment-to-const',
 								message: 'You are assigning to a const'
 							});
diff --git a/src/compiler/compile/nodes/shared/Expression.ts b/src/compiler/compile/nodes/shared/Expression.ts
index c3817dc3da..c105bc0e55 100644
--- a/src/compiler/compile/nodes/shared/Expression.ts
+++ b/src/compiler/compile/nodes/shared/Expression.ts
@@ -147,13 +147,13 @@ export default class Expression {
 						} else {
 							component.add_reference(node, name);
 
-                            const variable = component.var_lookup.get(name);
+							const variable = component.var_lookup.get(name);
 
 							if (variable) {
 								variable[deep ? 'mutated' : 'reassigned'] = true;
 
 								if (!deep && variable.writable === false) {
-									component.warn(node as any, {
+									component.error(node as any, {
 										code: 'assignment-to-const',
 										message: 'You are assigning to a const'
 									});
diff --git a/test/validator/samples/assignment-to-const-2/errors.json b/test/validator/samples/assignment-to-const-2/errors.json
new file mode 100644
index 0000000000..b8da2a3d8e
--- /dev/null
+++ b/test/validator/samples/assignment-to-const-2/errors.json
@@ -0,0 +1,17 @@
+[
+	{
+		"code": "assignment-to-const",
+		"message": "You are assigning to a const",
+		"start": {
+			"line": 13,
+			"column": 24,
+			"character": 282
+		},
+		"end": {
+			"line": 13,
+			"column": 35,
+			"character": 293
+		},
+		"pos": 282
+	}
+]
\ No newline at end of file
diff --git a/test/validator/samples/assignment-to-const-2/input.svelte b/test/validator/samples/assignment-to-const-2/input.svelte
new file mode 100644
index 0000000000..433c6d0076
--- /dev/null
+++ b/test/validator/samples/assignment-to-const-2/input.svelte
@@ -0,0 +1,15 @@
+<script>
+	const immutable = 0;
+
+	const obj1 = { prop: true };
+	const obj2 = { prop: 0 }
+</script>
+
+<!-- should not error -->
+<button on:click={() => obj1.prop = false}>click</button>
+<button on:click={() => obj2.prop++}>click</button>
+
+<!-- should error -->
+<button on:click={() => immutable++}>click</button>
+
+
diff --git a/test/validator/samples/assignment-to-const/errors.json b/test/validator/samples/assignment-to-const/errors.json
new file mode 100644
index 0000000000..9e673499f0
--- /dev/null
+++ b/test/validator/samples/assignment-to-const/errors.json
@@ -0,0 +1,17 @@
+[
+	{
+		"code": "assignment-to-const",
+		"message": "You are assigning to a const",
+		"start": {
+			"line": 16,
+			"column": 2,
+			"character": 237
+		},
+		"end": {
+			"line": 16,
+			"column": 18,
+			"character": 253
+		},
+		"pos": 237
+	}
+]
\ No newline at end of file
diff --git a/test/validator/samples/assignment-to-const/input.svelte b/test/validator/samples/assignment-to-const/input.svelte
index b685507b56..fa688a1202 100644
--- a/test/validator/samples/assignment-to-const/input.svelte
+++ b/test/validator/samples/assignment-to-const/input.svelte
@@ -1,34 +1,24 @@
 <script>
-	const immutable1 = false;
-	const immutable2 = 0;
+	const immutable = false;
 
-	// these ones should not warn
 	const obj1 = { prop: true };
 	const obj2 = { prop: 0 };
 
-	function func1() {
-		immutable1 = true
+	function funcShouldNotError() {
+		obj1.prop = false;
 	}
 
-	function func2() {
-		immutable2++;
+	function funcShouldNotError2() {
+		obj2.prop++;
 	}
 
-	function func3() {
-		obj1.prop = false;
+	function funcShouldError() {
+		immutable = true
 	}
 
-	function func4() {
-		obj2.prop++;
-	}
+	
 </script>
 
-<button on:click={func1}>click</button>
-<button on:click={func2}>click</button>
-<button on:click={func3}>click</button>
-<button on:click={func4}>click</button>
-
-<button on:click={() => immutable2 = true}>click</button>
-<button on:click={() => immutable2++}>click</button>
-<button on:click={() => obj1.prop = false}>click</button>
-<button on:click={() => obj2.prop++}>click</button>
\ No newline at end of file
+<button on:click={funcShouldNotError}>click</button>
+<button on:click={funcShouldNotError2}>click</button>
+<button on:click={funcShouldError}>click</button>
diff --git a/test/validator/samples/assignment-to-const/warnings.json b/test/validator/samples/assignment-to-const/warnings.json
deleted file mode 100644
index fac54a6058..0000000000
--- a/test/validator/samples/assignment-to-const/warnings.json
+++ /dev/null
@@ -1,62 +0,0 @@
-[
-	{
-		"code": "assignment-to-const",
-		"message": "You are assigning to a const",
-		"start": {
-			"line": 31,
-			"column": 24,
-			"character": 512
-		},
-		"end": {
-			"line": 31,
-			"column": 41,
-			"character": 529
-		},
-		"pos": 512
-	},
-	{
-		"code": "assignment-to-const",
-		"message": "You are assigning to a const",
-		"start": {
-			"line": 32,
-			"column": 24,
-			"character": 570
-		},
-		"end": {
-			"line": 32,
-			"column": 36,
-			"character": 582
-		},
-		"pos": 570
-	},
-	{
-		"code": "assignment-to-const",
-		"message": "You are assigning to a const",
-		"start": {
-			"line": 10,
-			"column": 2,
-			"character": 171
-		},
-		"end": {
-			"line": 10,
-			"column": 19,
-			"character": 188
-		},
-		"pos": 171
-	},
-	{
-		"code": "assignment-to-const",
-		"message": "You are assigning to a const",
-		"start": {
-			"line": 14,
-			"column": 2,
-			"character": 215
-		},
-		"end": {
-			"line": 14,
-			"column": 14,
-			"character": 227
-		},
-		"pos": 215
-	}
-]
\ No newline at end of file