diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..edae489
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1 @@
+export { default } from "./src/cssHexColorToRGBA.js";
diff --git a/index.js b/index.js
index cc9d02f..1d155b3 100644
--- a/index.js
+++ b/index.js
@@ -1,2 +1,2 @@
-export { default } from "./src/cssHexColorToRGB.js";
+export { default } from "./src/cssHexColorToRGBA.js";
 
diff --git a/src/cssHexColorToRGB.js b/src/cssHexColorToRGB.js
deleted file mode 100644
index 869b6b9..0000000
--- a/src/cssHexColorToRGB.js
+++ /dev/null
@@ -1,17 +0,0 @@
-import isCSSHexColor from "@chriscodesthings/is-css-hex-color";
-import expandCSSHexColor from "@chriscodesthings/expand-css-hex-color";
-
-function hexToDec(h) {
-    return parseInt(h, 16);
-}
-
-export default function (col) {
-    if (!isCSSHexColor(col)) {
-        return;
-    }
-
-    const hex = (expandCSSHexColor(col) + "ff").slice(1, 9);
-    const [r, g, b, a] = [hex.slice(0, 2), hex.slice(2, 4), hex.slice(4, 6), hex.slice(6, 8)];
-
-    return [hexToDec(r), hexToDec(g), hexToDec(b), Math.round((hexToDec(a) / 255) * 100) / 100];
-}
diff --git a/src/cssHexColorToRGBA.d.ts b/src/cssHexColorToRGBA.d.ts
new file mode 100644
index 0000000..de61f9e
--- /dev/null
+++ b/src/cssHexColorToRGBA.d.ts
@@ -0,0 +1,6 @@
+/**
+ * Converts a colour from a CSS hex colour code to an RGBA array
+ * @param {string} col CSS hex colour code
+ * @returns {[number, number, number, number]}
+ */
+export default function _default(col: string): [number, number, number, number];
diff --git a/src/cssHexColorToRGBA.js b/src/cssHexColorToRGBA.js
new file mode 100644
index 0000000..30b39be
--- /dev/null
+++ b/src/cssHexColorToRGBA.js
@@ -0,0 +1,19 @@
+// @ts-check
+
+import expandCSSHexColor from "@chriscodesthings/expand-css-hex-color";
+import { roundToPrecision } from "more-rounding";
+
+/**
+ * Converts a colour from a CSS hex colour code to an RGBA array
+ * @param {string} col CSS hex colour code
+ * @returns {[number, number, number, number]}
+ */
+export default function (col) {
+    const hex = expandCSSHexColor(col).slice(1);
+    const r = parseInt(hex.slice(0, 2), 16);
+    const g = parseInt(hex.slice(2, 4), 16);
+    const b = parseInt(hex.slice(4, 6), 16);
+    const a = roundToPrecision(parseInt(hex.slice(6, 8), 16) / 255, 2);
+
+    return [r, g, b, a];
+}