diff --git a/lib/rules/length-zero-no-unit/README.md b/lib/rules/length-zero-no-unit/README.md
index 0b3591f7fc..f0e749b6d9 100644
--- a/lib/rules/length-zero-no-unit/README.md
+++ b/lib/rules/length-zero-no-unit/README.md
@@ -67,3 +67,23 @@ The following pattern is _not_ considered a violation:
 ```css
 a { --x: 0px; }
 ```
+
+### `ignoreFunctions: ["/regex/", /regex/, "string"]`
+
+Given:
+
+```json
+["var", "/^--/"]
+```
+
+The following patterns are _not_ considered violations:
+
+<!-- prettier-ignore -->
+```css
+a { top: var(--foo, 0px); }
+```
+
+<!-- prettier-ignore -->
+```css
+a { top: --bar(0px); }
+```
diff --git a/lib/rules/length-zero-no-unit/__tests__/index.js b/lib/rules/length-zero-no-unit/__tests__/index.js
index d14d5def39..9c0685890a 100644
--- a/lib/rules/length-zero-no-unit/__tests__/index.js
+++ b/lib/rules/length-zero-no-unit/__tests__/index.js
@@ -608,6 +608,30 @@ testRule({
 	],
 });
 
+testRule({
+	ruleName,
+	config: [true, { ignoreFunctions: ['var', /^--/] }],
+	fix: true,
+	accept: [
+		{
+			code: 'a { top: var(--foo, 0px); }',
+		},
+		{
+			code: 'a { top: --bar(0px); }',
+		},
+	],
+	reject: [
+		{
+			code: 'a { margin: var(--foo, 0px) 0px --bar(0px); }',
+			fixed: 'a { margin: var(--foo, 0px) 0 --bar(0px); }',
+
+			message: messages.rejected,
+			line: 1,
+			column: 30,
+		},
+	],
+});
+
 testRule({
 	ruleName,
 	config: [true],
diff --git a/lib/rules/length-zero-no-unit/index.js b/lib/rules/length-zero-no-unit/index.js
index 5daf8e8eb2..aad1ea58f2 100644
--- a/lib/rules/length-zero-no-unit/index.js
+++ b/lib/rules/length-zero-no-unit/index.js
@@ -2,6 +2,7 @@
 
 'use strict';
 
+const _ = require('lodash');
 const valueParser = require('postcss-value-parser');
 
 const atRuleParamIndex = require('../../utils/atRuleParamIndex');
@@ -37,6 +38,7 @@ function rule(primary, secondary, context) {
 				actual: secondary,
 				possible: {
 					ignore: ['custom-properties'],
+					ignoreFunctions: [_.isString, _.isRegExp],
 				},
 				optional: true,
 			},
@@ -51,6 +53,9 @@ function rule(primary, secondary, context) {
 
 			if (isMathFunction(valueNode)) return false;
 
+			if (isFunction(valueNode) && optionsMatches(secondary, 'ignoreFunctions', value))
+				return false;
+
 			if (!isWord(valueNode)) return;
 
 			const numberUnit = valueParser.unit(value);
@@ -156,6 +161,10 @@ function isLength(unit) {
 	return keywordSets.lengthUnits.has(unit.toLowerCase());
 }
 
+function isFunction({ type }) {
+	return type === 'function';
+}
+
 function isFraction(unit) {
 	return unit.toLowerCase() === 'fr';
 }