diff --git a/.changeset/clean-snakes-cheat.md b/.changeset/clean-snakes-cheat.md
new file mode 100644
index 0000000000..f5997ce3f0
--- /dev/null
+++ b/.changeset/clean-snakes-cheat.md
@@ -0,0 +1,5 @@
+---
+"stylelint": patch
+---
+
+Fixed: `declaration-property-value-no-unknown` parse error for `alpha(opacity=n)` to report as violation
diff --git a/lib/rules/declaration-property-value-no-unknown/__tests__/index.js b/lib/rules/declaration-property-value-no-unknown/__tests__/index.js
index 99748a5b8d..7a12acfb53 100644
--- a/lib/rules/declaration-property-value-no-unknown/__tests__/index.js
+++ b/lib/rules/declaration-property-value-no-unknown/__tests__/index.js
@@ -124,6 +124,14 @@ testRule({
 			endLine: 1,
 			endColumn: 17,
 		},
+		{
+			code: 'a { filter: alpha(opacity=30); }',
+			message: messages.rejectedParseError('filter', 'alpha(opacity=30)'),
+			line: 1,
+			column: 13,
+			endLine: 1,
+			endColumn: 30,
+		},
 	],
 });
 
diff --git a/lib/rules/declaration-property-value-no-unknown/index.js b/lib/rules/declaration-property-value-no-unknown/index.js
index 6c095e1e8c..0f8902b32f 100644
--- a/lib/rules/declaration-property-value-no-unknown/index.js
+++ b/lib/rules/declaration-property-value-no-unknown/index.js
@@ -19,6 +19,8 @@ const ruleName = 'declaration-property-value-no-unknown';
 
 const messages = ruleMessages(ruleName, {
 	rejected: (property, value) => `Unexpected unknown value "${value}" for property "${property}"`,
+	rejectedParseError: (property, value) =>
+		`Cannot parse property value "${value}" for property "${property}"`,
 });
 
 const meta = {
@@ -91,9 +93,16 @@ const rule = (primary, secondaryOptions) => {
 
 				if (containsUnsupportedFunction(cssTreeValueNode)) return;
 			} catch (e) {
-				result.warn(`Cannot parse property value "${value}"`, {
+				const index = declarationValueIndex(decl);
+				const endIndex = index + value.length;
+
+				report({
+					message: messages.rejectedParseError(prop, value),
 					node: decl,
-					stylelintType: 'parseError',
+					index,
+					endIndex,
+					result,
+					ruleName,
 				});
 
 				return;