diff --git a/.changeset/heavy-pandas-cheer.md b/.changeset/heavy-pandas-cheer.md
new file mode 100644
index 0000000000..ce4a855fe6
--- /dev/null
+++ b/.changeset/heavy-pandas-cheer.md
@@ -0,0 +1,5 @@
+---
+"stylelint": patch
+---
+
+Fixed: `custom-property-no-missing-var-function` performance
diff --git a/lib/rules/custom-property-no-missing-var-function/index.js b/lib/rules/custom-property-no-missing-var-function/index.js
index 6477997df1..f6378ff7f3 100644
--- a/lib/rules/custom-property-no-missing-var-function/index.js
+++ b/lib/rules/custom-property-no-missing-var-function/index.js
@@ -3,7 +3,6 @@
 const valueParser = require('postcss-value-parser');
 
 const declarationValueIndex = require('../../utils/declarationValueIndex');
-const isCustomProperty = require('../../utils/isCustomProperty');
 const report = require('../../utils/report');
 const ruleMessages = require('../../utils/ruleMessages');
 const validateOptions = require('../../utils/validateOptions');
@@ -32,12 +31,15 @@ const rule = (primary) => {
 			knownCustomProperties.add(atRule.params);
 		});
 
-		root.walkDecls(({ prop }) => {
-			if (isCustomProperty(prop)) knownCustomProperties.add(prop);
+		root.walkDecls(/^--/, ({ prop }) => {
+			knownCustomProperties.add(prop);
 		});
 
 		root.walkDecls((decl) => {
 			const { value } = decl;
+
+			if (!value.includes('--')) return;
+
 			const parsedValue = valueParser(value);
 
 			parsedValue.walk((node) => {