diff --git a/src/style-spec/error/parsing_error.js b/src/style-spec/error/parsing_error.js
index d5c20f58583..cd2cb6bce7f 100644
--- a/src/style-spec/error/parsing_error.js
+++ b/src/style-spec/error/parsing_error.js
@@ -1,9 +1,13 @@
+// @flow
 
-function ParsingError(error) {
-    this.error = error;
-    this.message = error.message;
-    const match = error.message.match(/line (\d+)/);
-    this.line = match ? parseInt(match[1], 10) : 0;
-}
+export default class ParsingError extends Error {
+    error: Error;
+    line: number;
 
-export default ParsingError;
+    constructor(error: Error) {
+        super(error.message);
+        this.error = error;
+        const match = error.message.match(/line (\d+)/);
+        this.line = match ? parseInt(match[1], 10) : 0;
+    }
+}
diff --git a/src/style-spec/error/validation_error.js b/src/style-spec/error/validation_error.js
index 0ab246138a7..b57ad89b854 100644
--- a/src/style-spec/error/validation_error.js
+++ b/src/style-spec/error/validation_error.js
@@ -1,7 +1,11 @@
+// @flow
 
-export default class ValidationError {
-    constructor(key, value, message, identifier) {
-        this.message = (key ? `${key}: ` : '') + message;
+export default class ValidationError extends Error {
+    identifier: ?string;
+    line: ?number;
+
+    constructor(key: string | null, value?: any, message?: string, identifier?: string) {
+        super([key, message].filter(a => a).join(': '));
         if (identifier) this.identifier = identifier;
 
         if (value !== null && value !== undefined && value.__line__) {
diff --git a/src/style-spec/expression/types/formatted.js b/src/style-spec/expression/types/formatted.js
index 224594f5360..726242ea30f 100644
--- a/src/style-spec/expression/types/formatted.js
+++ b/src/style-spec/expression/types/formatted.js
@@ -60,14 +60,14 @@ export default class Formatted {
     }
 
     serialize(): Array<mixed> {
-        const serialized = ["format"];
+        const serialized: Array<mixed> = ["format"];
         for (const section of this.sections) {
             if (section.image) {
                 serialized.push(["image", section.image.name]);
                 continue;
             }
             serialized.push(section.text);
-            const options = {};
+            const options: { [key: string]: mixed } = {};
             if (section.fontStack) {
                 options["text-font"] = ["literal", section.fontStack.split(',')];
             }
@@ -75,7 +75,7 @@ export default class Formatted {
                 options["font-scale"] = section.scale;
             }
             if (section.textColor) {
-                options["text-color"] = ["rgba"].concat(section.textColor.toArray());
+                options["text-color"] = (["rgba"]: Array<mixed>).concat(section.textColor.toArray());
             }
             serialized.push(options);
         }
diff --git a/src/style-spec/expression/types/resolved_image.js b/src/style-spec/expression/types/resolved_image.js
index 2919b1e8a5b..b5f31ed55bb 100644
--- a/src/style-spec/expression/types/resolved_image.js
+++ b/src/style-spec/expression/types/resolved_image.js
@@ -22,7 +22,7 @@ export default class ResolvedImage {
         return new ResolvedImage({name, available: false});
     }
 
-    serialize(): Array<mixed> {
+    serialize(): Array<string> {
         return ["image", this.name];
     }
 }
diff --git a/src/style-spec/expression/values.js b/src/style-spec/expression/values.js
index 6b5539f89fa..6c5e5407dc9 100644
--- a/src/style-spec/expression/values.js
+++ b/src/style-spec/expression/values.js
@@ -10,7 +10,7 @@ import {NullType, NumberType, StringType, BooleanType, ColorType, ObjectType, Va
 
 import type {Type} from './types';
 
-export function validateRGBA(r: mixed, g: mixed, b: mixed, a?: mixed): ?string {
+export function validateRGBA(r: mixed, g: mixed, b: mixed, a?: mixed): string | null {
     if (!(
         typeof r === 'number' && r >= 0 && r <= 255 &&
         typeof g === 'number' && g >= 0 && g <= 255 &&
@@ -86,7 +86,7 @@ export function typeOf(value: Value): Type {
         return ResolvedImageType;
     } else if (Array.isArray(value)) {
         const length = value.length;
-        let itemType: ?Type;
+        let itemType: Type | typeof undefined;
 
         for (const item of value) {
             const t = typeOf(item);
diff --git a/src/style-spec/util/color.js b/src/style-spec/util/color.js
index 57e56165dd3..a8e59b74f05 100644
--- a/src/style-spec/util/color.js
+++ b/src/style-spec/util/color.js
@@ -35,7 +35,7 @@ class Color {
      * Parses valid CSS color strings and returns a `Color` instance.
      * @returns A `Color` instance, or `undefined` if the input is not a valid color string.
      */
-    static parse(input: ?string): Color | void {
+    static parse(input?: string | Color | null): Color | void {
         if (!input) {
             return undefined;
         }
diff --git a/src/style-spec/util/color_spaces.js b/src/style-spec/util/color_spaces.js
index 954de5c93a5..21ee75b0c69 100644
--- a/src/style-spec/util/color_spaces.js
+++ b/src/style-spec/util/color_spaces.js
@@ -30,19 +30,19 @@ const Xn = 0.950470, // D65 standard referent
     rad2deg = 180 / Math.PI;
 
 // Utilities
-function xyz2lab(t) {
+function xyz2lab(t: number) {
     return t > t3 ? Math.pow(t, 1 / 3) : t / t2 + t0;
 }
 
-function lab2xyz(t) {
+function lab2xyz(t: number) {
     return t > t1 ? t * t * t : t2 * (t - t0);
 }
 
-function xyz2rgb(x) {
+function xyz2rgb(x: number) {
     return 255 * (x <= 0.0031308 ? 12.92 * x : 1.055 * Math.pow(x, 1 / 2.4) - 0.055);
 }
 
-function rgb2xyz(x) {
+function rgb2xyz(x: number) {
     x /= 255;
     return x <= 0.04045 ? x / 12.92 : Math.pow((x + 0.055) / 1.055, 2.4);
 }
diff --git a/src/style-spec/util/extend.js b/src/style-spec/util/extend.js
index 3f041cc63b0..076b6f278a4 100644
--- a/src/style-spec/util/extend.js
+++ b/src/style-spec/util/extend.js
@@ -1,5 +1,6 @@
+// @flow
 
-export default function (output, ...inputs) {
+export default function (output: any, ...inputs: Array<any>) {
     for (const input of inputs) {
         for (const k in input) {
             output[k] = input[k];
diff --git a/src/style-spec/util/get_type.js b/src/style-spec/util/get_type.js
index c31925f35a3..18b03eb625e 100644
--- a/src/style-spec/util/get_type.js
+++ b/src/style-spec/util/get_type.js
@@ -1,5 +1,6 @@
+// @flow
 
-export default function getType(val) {
+export default function getType(val: mixed): string {
     if (val instanceof Number) {
         return 'number';
     } else if (val instanceof String) {
diff --git a/src/style-spec/util/unbundle_jsonlint.js b/src/style-spec/util/unbundle_jsonlint.js
index 0fd78107892..72eb2d92645 100644
--- a/src/style-spec/util/unbundle_jsonlint.js
+++ b/src/style-spec/util/unbundle_jsonlint.js
@@ -1,21 +1,19 @@
-function isPrimitive(value) {
-    return value instanceof Number || value instanceof String || value instanceof Boolean;
-}
+// @flow
 
 // Turn jsonlint-lines-primitives objects into primitive objects
-export function unbundle(value) {
-    if (isPrimitive(value)) {
+export function unbundle(value: mixed) {
+    if (value instanceof Number || value instanceof String || value instanceof Boolean) {
         return value.valueOf();
     } else {
         return value;
     }
 }
 
-export function deepUnbundle(value) {
+export function deepUnbundle(value: mixed): mixed {
     if (Array.isArray(value)) {
         return value.map(deepUnbundle);
-    } else if (value instanceof Object && !isPrimitive(value)) {
-        const unbundledValue = {};
+    } else if (value instanceof Object && !(value instanceof Number || value instanceof String || value instanceof Boolean)) {
+        const unbundledValue: { [key: string]: mixed } = {};
         for (const key in value) {
             unbundledValue[key] = deepUnbundle(value[key]);
         }
@@ -24,4 +22,3 @@ export function deepUnbundle(value) {
 
     return unbundle(value);
 }
-
diff --git a/test/unit/style-spec/validate.test.js b/test/unit/style-spec/validate.test.js
index 64fd3080d92..2e37799d656 100644
--- a/test/unit/style-spec/validate.test.js
+++ b/test/unit/style-spec/validate.test.js
@@ -6,6 +6,15 @@ import validate from '../../../src/style-spec/validate_style';
 
 const UPDATE = !!process.env.UPDATE;
 
+function sanitizeError(error) {
+    const sanitized = {};
+    sanitized.message = error.message;
+    for (const key in error) {
+        sanitized[key] = error[key];
+    }
+    return sanitized;
+}
+
 glob.sync(`${__dirname}/fixture/*.input.json`).forEach((file) => {
     test(path.basename(file), (t) => {
         const outputfile = file.replace('.input', '.output');
@@ -13,7 +22,7 @@ glob.sync(`${__dirname}/fixture/*.input.json`).forEach((file) => {
         const result = validate(style);
         if (UPDATE) fs.writeFileSync(outputfile, JSON.stringify(result, null, 2));
         const expect = JSON.parse(fs.readFileSync(outputfile));
-        t.deepEqual(result, expect);
+        t.deepEqual(result.map(sanitizeError), expect);
         t.end();
     });
 });
diff --git a/test/unit/style-spec/validate_mapbox_api_supported.test.js b/test/unit/style-spec/validate_mapbox_api_supported.test.js
index 810eb111cb6..37bd5e808ed 100644
--- a/test/unit/style-spec/validate_mapbox_api_supported.test.js
+++ b/test/unit/style-spec/validate_mapbox_api_supported.test.js
@@ -6,6 +6,15 @@ import validateMapboxApiSupported from '../../../src/style-spec/validate_mapbox_
 
 const UPDATE = !!process.env.UPDATE;
 
+function sanitizeError(error) {
+    const sanitized = {};
+    sanitized.message = error.message;
+    for (const key in error) {
+        sanitized[key] = error[key];
+    }
+    return sanitized;
+}
+
 glob.sync(`${__dirname}/fixture/*.input.json`).forEach((file) => {
     test(path.basename(file), (t) => {
         const outputfile = file.replace('.input', '.output-api-supported');
@@ -13,7 +22,7 @@ glob.sync(`${__dirname}/fixture/*.input.json`).forEach((file) => {
         const result = validateMapboxApiSupported(style);
         if (UPDATE) fs.writeFileSync(outputfile, JSON.stringify(result, null, 2));
         const expect = JSON.parse(fs.readFileSync(outputfile));
-        t.deepEqual(result, expect);
+        t.deepEqual(result.map(sanitizeError), expect);
         t.end();
     });
 });