diff --git a/lib/rules/function-no-unknown/README.md b/lib/rules/function-no-unknown/README.md
index bd6af56175..2b3200f2c0 100644
--- a/lib/rules/function-no-unknown/README.md
+++ b/lib/rules/function-no-unknown/README.md
@@ -35,3 +35,29 @@ a { transform: scale(1); }
 ```css
 a { transform: --custom-function(1); }
 ```
+
+## Optional secondary options
+
+### `ignoreFunctions: ["/regex/", /regex/, "non-regex"]`
+
+Ignore the specified functions.
+
+For example, with `true`.
+
+Given:
+
+```json
+["theme", "/^foo-/"]
+```
+
+The following patterns are _not_ considered problems:
+
+<!-- prettier-ignore -->
+```css
+a { transform: theme(1); }
+```
+
+<!-- prettier-ignore -->
+```css
+a { transform: foo-func(1); }
+```
diff --git a/lib/rules/function-no-unknown/__tests__/index.js b/lib/rules/function-no-unknown/__tests__/index.js
index a3991768b2..97ca4f9c8e 100644
--- a/lib/rules/function-no-unknown/__tests__/index.js
+++ b/lib/rules/function-no-unknown/__tests__/index.js
@@ -56,3 +56,42 @@ testRule({
 		},
 	],
 });
+
+testRule({
+	ruleName,
+	config: [true, { ignoreFunctions: ['theme', '/^foo-/', /^bar$/i] }],
+	skipBasicChecks: true,
+
+	accept: [
+		{
+			code: 'a { transform: translate(1px); }',
+		},
+		{
+			code: 'a { transform: theme(1px); }',
+		},
+		{
+			code: 'a { transform: foo-func(1px); }',
+		},
+		{
+			code: 'a { transform: bar(1px); }',
+		},
+		{
+			code: 'a { transform: BAR(1px); }',
+		},
+	],
+
+	reject: [
+		{
+			code: 'a { transform: unknown(1px); }',
+			message: messages.rejected('unknown'),
+			line: 1,
+			column: 16,
+		},
+		{
+			code: 'a { transform: theme-custom(1px); }',
+			message: messages.rejected('theme-custom'),
+			line: 1,
+			column: 16,
+		},
+	],
+});
diff --git a/lib/rules/function-no-unknown/index.js b/lib/rules/function-no-unknown/index.js
index 3d861d589a..03d21fd2fd 100644
--- a/lib/rules/function-no-unknown/index.js
+++ b/lib/rules/function-no-unknown/index.js
@@ -6,11 +6,13 @@ const valueParser = require('postcss-value-parser');
 const functionsListPath = require('css-functions-list');
 
 const declarationValueIndex = require('../../utils/declarationValueIndex');
+const optionsMatches = require('../../utils/optionsMatches');
 const report = require('../../utils/report');
 const ruleMessages = require('../../utils/ruleMessages');
 const validateOptions = require('../../utils/validateOptions');
 const isStandardSyntaxFunction = require('../../utils/isStandardSyntaxFunction');
 const isCustomFunction = require('../../utils/isCustomFunction');
+const { isRegExp, isString } = require('../../utils/validateTypes');
 
 const ruleName = 'function-no-unknown';
 
@@ -23,9 +25,20 @@ const meta = {
 };
 
 /** @type {import('stylelint').Rule} */
-const rule = (primary) => {
+const rule = (primary, secondaryOptions) => {
 	return (root, result) => {
-		const validOptions = validateOptions(result, ruleName, { actual: primary });
+		const validOptions = validateOptions(
+			result,
+			ruleName,
+			{ actual: primary },
+			{
+				actual: secondaryOptions,
+				possible: {
+					ignoreFunctions: [isString, isRegExp],
+				},
+				optional: true,
+			},
+		);
 
 		if (!validOptions) {
 			return;
@@ -50,6 +63,10 @@ const rule = (primary) => {
 					return;
 				}
 
+				if (optionsMatches(secondaryOptions, 'ignoreFunctions', node.value)) {
+					return;
+				}
+
 				if (functionsList.includes(node.value.toLowerCase())) {
 					return;
 				}