diff --git a/src/parse.js b/src/parse.js
index af9cfa843..6a5cffcf8 100644
--- a/src/parse.js
+++ b/src/parse.js
@@ -74,7 +74,7 @@ export default function parse (str, {meta} = {}) {
 
 		let alpha = 1;
 
-		if (format.lastAlpha || env.parsed.lastAlpha) {
+		if (format.alpha === true || env.parsed.lastAlpha) {
 			alpha = env.parsed.args.pop();
 		}
 
diff --git a/src/serialize.js b/src/serialize.js
index 15cd43046..f67e38ddd 100644
--- a/src/serialize.js
+++ b/src/serialize.js
@@ -8,16 +8,19 @@ import clone from "./clone.js";
 
 /**
  * Generic toString() method, outputs a color(spaceId ...coords) function, a functional syntax, or custom formats defined by the color space
- * @param {Object} options
- * @param {number} options.precision - Significant digits
- * @param {boolean} options.inGamut - Adjust coordinates to fit in gamut first? [default: false]
+ * @param {Object} [options]
+ * @param {number} [options.precision] - Significant digits
+ * @param {boolean} [options.inGamut=false] - Adjust coordinates to fit in gamut first?
+ * @param {string} [options.format="default"] - Output format id, default is "default"
+ * @param {string} [options.coords] - Coordinate format to override the default
+ * @param {string | boolean | {type: string, include: boolean}} [options.alpha] - Alpha format
  */
 export default function serialize (color, {
 	precision = defaults.precision,
 	format = "default",
 	inGamut = true,
-	coordTypes,
-	alphaType,
+	coords: coordFormat,
+	alpha: alphaFormat,
 	...customOptions
 } = {}) {
 	let ret;
@@ -56,7 +59,7 @@ export default function serialize (color, {
 		// Functional syntax
 		let name = format.name || "color";
 
-		let args = format.serializeCoords(coords, precision, coordTypes);
+		let args = format.serializeCoords(coords, precision, coordFormat);
 
 		if (name === "color") {
 			// If output is a color() function, add colorspace id as first argument
@@ -65,11 +68,30 @@ export default function serialize (color, {
 		}
 
 		let alpha = color.alpha;
-		if (precision !== null) {
-			alpha = util.serializeNumber(alpha, {precision});
+
+		if (alphaFormat !== undefined && !(typeof alphaFormat === "object")) {
+			alphaFormat = typeof alphaFormat === "string" ? {type: alphaFormat} : {include: alphaFormat};
+		}
+
+		let alphaType = alphaFormat?.type ?? "<number>";
+		let serializeAlpha = alphaFormat?.include === true || format.alpha === true || (alphaFormat?.include !== false && format.alpha !== false && alpha < 1);
+		let strAlpha = "";
+
+		if (serializeAlpha) {
+			if (precision !== null) {
+				let unit;
+
+				if (alphaType === "<percentage>") {
+					unit = "%";
+					alpha *= 100;
+				}
+
+				alpha = util.serializeNumber(alpha, {precision});
+			}
+
+			strAlpha = `${format.commas ? "," : " /"} ${alpha}`;
 		}
 
-		let strAlpha = color.alpha >= 1 || format.noAlpha ? "" : `${format.commas ? "," : " /"} ${alpha}`;
 		ret = `${name}(${args.join(format.commas ? ", " : " ")}${strAlpha})`;
 	}
 
diff --git a/src/spaces/hsl.js b/src/spaces/hsl.js
index 7cb5410bd..7ec82a878 100644
--- a/src/spaces/hsl.js
+++ b/src/spaces/hsl.js
@@ -85,7 +85,7 @@ export default new ColorSpace({
 		"hsla": {
 			coords: ["<number> | <angle>", "<percentage>", "<percentage>"],
 			commas: true,
-			lastAlpha: true,
+			alpha: true,
 		},
 	},
 });
diff --git a/src/spaces/srgb.js b/src/spaces/srgb.js
index 692abf0b4..f47aaaae8 100644
--- a/src/spaces/srgb.js
+++ b/src/spaces/srgb.js
@@ -47,13 +47,13 @@ export default new RGBColorSpace({
 			name: "rgb",
 			commas: true,
 			coords: coordGrammarNumber,
-			noAlpha: true,
+			alpha: false,
 		},
 		"color": { /* use defaults */ },
 		"rgba": {
 			coords: coordGrammar,
 			commas: true,
-			lastAlpha: true,
+			alpha: true,
 		},
 		"rgba_number": {
 			name: "rgba",
diff --git a/test/serialize.js b/test/serialize.js
index 5cdc6dc35..eb54d965e 100644
--- a/test/serialize.js
+++ b/test/serialize.js
@@ -33,7 +33,45 @@ const tests = {
 					args: ["oklab", [.65, 0.2, .1]],
 					expect: "oklab(65% 0.2 0.1)",
 				},
-			]
+			],
+		},
+		{
+			name: "With alpha",
+			tests: [
+				{
+					args: ["srgb", [1, 0.5, 0], .5],
+					expect: "rgb(100% 50% 0% / 0.5)",
+				},
+				{
+					args: ["lch", [65, 20, 90], .5],
+					expect: "lch(65% 20 90 / 0.5)",
+				},
+				{
+					args: ["lab", [65, 20, 90], .5],
+					expect: "lab(65% 20 90 / 0.5)",
+				},
+				{
+					args: ["oklch", [.65, 0.2, 90], .5],
+					expect: "oklch(65% 0.2 90 / 0.5)",
+				},
+				{
+					args: ["oklab", [.65, 0.2, .1], .5],
+					expect: "oklab(65% 0.2 0.1 / 0.5)",
+				},
+			],
+		},
+		{
+			name: "Mandatory alpha",
+			tests: [
+				{
+					args: ["srgb", [1, 0.5, 0], 1, {format: "rgba"}],
+					expect: "rgba(100%, 50%, 0%, 1)",
+				},
+				{
+					args: ["hsl", [180, 50, 50], 1, {format: "hsla"}],
+					expect: "hsla(180, 50%, 50%, 1)",
+				},
+			],
 		},
 		{
 			name: "Alternate formats",
@@ -43,8 +81,18 @@ const tests = {
 					args: ["srgb", [1, 0.5, 0], 1, {format: "hex"}],
 					expect: "#ff8000",
 				},
-			]
-		}
+			],
+		},
+		{
+			name: "Custom alpha format",
+			tests: [
+				{
+					name: "Force alpha",
+					args: ["srgb", [1, 0.5, 0], 1, {alpha: true}],
+					expect: "rgb(100% 50% 0% / 1)",
+				},
+			],
+		},
 	],
 };
 
diff --git a/types/src/space.d.ts b/types/src/space.d.ts
index 4b2e52876..9bbdcb8d0 100644
--- a/types/src/space.d.ts
+++ b/types/src/space.d.ts
@@ -21,10 +21,8 @@ export interface Format {
 	toGamut?: boolean | undefined;
 	/** Whether commas should separate arguments for a format */
 	commas?: boolean | undefined;
-	/** Whether the last coordinate is the alpha coordinate */
-	lastAlpha?: boolean | undefined;
-	/** Whether the format has an alpha channel */
-	noAlpha?: boolean | undefined;
+	/** Whether to always have alpha at the end (true), never (false), or auto (undefined) */
+	alpha?: boolean | undefined;
 	test?: ((str: string) => boolean) | undefined;
 	/** Function to parse a string into a color */
 	parse?: ((str: string) => ColorConstructor) | undefined;