diff --git a/src/index.js b/src/index.js
index 709b1cd..5af4818 100644
--- a/src/index.js
+++ b/src/index.js
@@ -128,6 +128,15 @@ const processor = postcss.plugin('postcss-modules-scope', function(options) {
 
     // Find any :local classes
     css.walkRules(rule => {
+      if (
+        rule.nodes &&
+        rule.selector.slice(0, 2) === '--' &&
+        rule.selector.slice(-1) === ':'
+      ) {
+        // ignore custom property set
+        return;
+      }
+
       let parsedSelector = selectorParser().astSync(rule);
 
       rule.selector = traverseNode(parsedSelector.clone()).toString();
diff --git a/test/test-cases/ignore-custom-property-set/expected.css b/test/test-cases/ignore-custom-property-set/expected.css
new file mode 100644
index 0000000..5d4cb10
--- /dev/null
+++ b/test/test-cases/ignore-custom-property-set/expected.css
@@ -0,0 +1,6 @@
+:root {
+    --title-align: center;
+    --sr-only: {
+        position: absolute;
+    }
+}
diff --git a/test/test-cases/ignore-custom-property-set/source.css b/test/test-cases/ignore-custom-property-set/source.css
new file mode 100644
index 0000000..5d4cb10
--- /dev/null
+++ b/test/test-cases/ignore-custom-property-set/source.css
@@ -0,0 +1,6 @@
+:root {
+    --title-align: center;
+    --sr-only: {
+        position: absolute;
+    }
+}