diff --git a/packages/postcss-minify-selectors/src/index.js b/packages/postcss-minify-selectors/src/index.js
index 8c1e83613..9276ff2be 100644
--- a/packages/postcss-minify-selectors/src/index.js
+++ b/packages/postcss-minify-selectors/src/index.js
@@ -131,17 +131,18 @@ function pseudo(selector) {
     return;
   }
 
-  const uniques = new Set();
-
   selector.walk((child) => {
-    if (child.type === 'selector') {
-      const childStr = String(child);
-
-      if (!uniques.has(childStr)) {
-        uniques.add(childStr);
-      } else {
-        child.remove();
-      }
+    if (child.type === 'selector' && child.parent) {
+      const uniques = new Set();
+      child.parent.each((sibling) => {
+        const siblingStr = String(sibling);
+
+        if (!uniques.has(siblingStr)) {
+          uniques.add(siblingStr);
+        } else {
+          sibling.remove();
+        }
+      });
     }
   });
 
diff --git a/packages/postcss-minify-selectors/test/index.js b/packages/postcss-minify-selectors/test/index.js
index b57b63c02..bdb68fe8d 100644
--- a/packages/postcss-minify-selectors/test/index.js
+++ b/packages/postcss-minify-selectors/test/index.js
@@ -540,4 +540,12 @@ test(
   'should handle attribute selector and namespace #3',
   passthroughCSS('div[att] {  }')
 );
+test(
+  'should not remove equal selectors parts which aren\'t duplicates #1402',
+  processCSS(':where(a,:not(a)) {  }', ':where(a,:not(a)) {  }')
+);
+test(
+  'should not remove equal selectors parts which aren\'t duplicates #1216',
+  processCSS(':where(:nth-child(7),:nth-child(7)~*) {  }', ':where(:nth-child(7),:nth-child(7)~*) {  }')
+);
 test.run();