diff --git a/packages/less/src/less/tree/expression.js b/packages/less/src/less/tree/expression.js
index 957505b87..121492f9c 100644
--- a/packages/less/src/less/tree/expression.js
+++ b/packages/less/src/less/tree/expression.js
@@ -45,7 +45,7 @@ Expression.prototype = Object.assign(new Node(), {
         if (inParenthesis) {
             context.outOfParenthesis();
         }
-        if (this.parens && this.parensInOp && !mathOn && !doubleParen 
+        if (this.parens && this.parensInOp && !mathOn && !doubleParen
             && (!(returnValue instanceof Dimension))) {
             returnValue = new Paren(returnValue);
         }
diff --git a/packages/less/src/less/tree/quoted.js b/packages/less/src/less/tree/quoted.js
index cb0d56b12..c6dbfd738 100644
--- a/packages/less/src/less/tree/quoted.js
+++ b/packages/less/src/less/tree/quoted.js
@@ -34,7 +34,15 @@ Quoted.prototype = Object.assign(new Node(), {
         const that = this;
         let value = this.value;
         const variableReplacement = function (_, name) {
-            const v = new Variable(`@${name}`, that.getIndex(), that.fileInfo()).eval(context, true);
+            let v;
+            try {
+                v = new Variable(`@${name}`, that.getIndex(), that.fileInfo()).eval(context, true);
+            } catch (e) {
+                if (e.type !== 'Name') {
+                    throw e;
+                }
+                return `@${name}`;
+            }
             return (v instanceof Quoted) ? v.value : v.toCSS();
         };
         const propertyReplacement = function (_, name) {
diff --git a/packages/less/test/browser/generator/runner.config.js b/packages/less/test/browser/generator/runner.config.js
index 8dc30ed58..f78d87e21 100644
--- a/packages/less/test/browser/generator/runner.config.js
+++ b/packages/less/test/browser/generator/runner.config.js
@@ -183,4 +183,4 @@ module.exports = {
             outfile: 'tmp/browser/test-runner-filemanager-plugin.html'
         }
     }
-}
\ No newline at end of file
+}
diff --git a/packages/test-data/css/_main/atrule-passthrough.css b/packages/test-data/css/_main/atrule-passthrough.css
new file mode 100644
index 000000000..db0bdd0dd
--- /dev/null
+++ b/packages/test-data/css/_main/atrule-passthrough.css
@@ -0,0 +1,5 @@
+.test {
+  --iron-autogrow-textarea: {
+    @apply --app-font-monospace;
+    };
+}
diff --git a/packages/test-data/less/_main/atrule-passthrough.less b/packages/test-data/less/_main/atrule-passthrough.less
new file mode 100644
index 000000000..25bea9210
--- /dev/null
+++ b/packages/test-data/less/_main/atrule-passthrough.less
@@ -0,0 +1,5 @@
+.test {
+  --iron-autogrow-textarea: {
+    @apply --app-font-monospace;
+    }
+}