diff --git a/src/rules/relative-font-units.js b/src/rules/relative-font-units.js
index 59d4d585..892a8ff4 100644
--- a/src/rules/relative-font-units.js
+++ b/src/rules/relative-font-units.js
@@ -139,8 +139,22 @@ export default {
 							child => child.type === "Identifier",
 						);
 						const percentageNode = value.children.find(
-							child => child.type === "Percentage",
+							(child, index) => {
+								const isPercentage =
+									child.type === "Percentage";
+								const previousNode = value.children[index - 1];
+
+								const previousNodeIsSlashOperator =
+									previousNode &&
+									previousNode.type === "Operator" &&
+									previousNode.value === "/";
+
+								return (
+									isPercentage && !previousNodeIsSlashOperator
+								);
+							},
 						);
+
 						let location;
 						let shouldReport = false;
 
diff --git a/tests/rules/relative-font-units.test.js b/tests/rules/relative-font-units.test.js
index 9bad3665..1fd3747b 100644
--- a/tests/rules/relative-font-units.test.js
+++ b/tests/rules/relative-font-units.test.js
@@ -50,6 +50,7 @@ ruleTester.run("relative-font-units", rule, {
 		"a { font: revert-layer Arial, sans-serif; }",
 		"a { font-size: unset; }",
 		"a { font: unset Arial, sans-serif; }",
+		"a { font: 1rem/120% Arial, sans-serif; }",
 		{
 			code: "a { font-size: 1em; }",
 			options: [
@@ -843,6 +844,24 @@ ruleTester.run("relative-font-units", rule, {
                 a {
                     font: 20% Arial, sans-serif;
                 }
+            `,
+			options: [
+				{
+					allowUnits: ["em"],
+				},
+			],
+			errors: [
+				{
+					messageId: "allowedFontUnits",
+					data: { allowedFontUnits: "em" },
+				},
+			],
+		},
+		{
+			code: dedent`
+                a {
+                    font: 1rem/120% Arial, sans-serif;
+                }
             `,
 			options: [
 				{