diff --git a/exist-core/src/main/antlr/org/exist/xquery/parser/XQueryTree.g b/exist-core/src/main/antlr/org/exist/xquery/parser/XQueryTree.g
index 20308296806..3109d357158 100644
--- a/exist-core/src/main/antlr/org/exist/xquery/parser/XQueryTree.g
+++ b/exist-core/src/main/antlr/org/exist/xquery/parser/XQueryTree.g
@@ -2989,14 +2989,22 @@ throws PermissionDeniedException, EXistException, XPathException
                         rs.setAbbreviated(true);
                     }
 
-                } else {
+                } else if (rightStep instanceof VariableReference) {
                     rightStep.setPrimaryAxis(Constants.DESCENDANT_SELF_AXIS);
-                    if(rightStep instanceof VariableReference) {
-                        rightStep = new SimpleStep(context, Constants.DESCENDANT_SELF_AXIS, rightStep);
-                        path.replaceLastExpression(rightStep);
-                    } else if (rightStep instanceof FilteredExpression)
-                        ((FilteredExpression)rightStep).setAbbreviated(true);
-
+                    rightStep = new SimpleStep(context, Constants.DESCENDANT_SELF_AXIS, rightStep);
+                    path.replaceLastExpression(rightStep);
+                } else if (rightStep instanceof FilteredExpression) {
+                    rightStep.setPrimaryAxis(Constants.DESCENDANT_SELF_AXIS);
+                    ((FilteredExpression)rightStep).setAbbreviated(true);
+                } else {
+                    // For other non-LocationStep expressions (e.g., PathExpr wrapping
+                    // parenthesized expressions like //(@x) or //(a | b)), insert an
+                    // explicit descendant-or-self::node() step. We must NOT call
+                    // setPrimaryAxis here because it would corrupt inner axes (e.g.,
+                    // overwriting an attribute axis in //(@x)).
+                    LocationStep descStep = new LocationStep(context, Constants.DESCENDANT_SELF_AXIS, new TypeTest(Type.NODE));
+                    path.replaceLastExpression(descStep);
+                    path.add(rightStep);
                 }
             }
         )?
diff --git a/exist-core/src/test/java/org/exist/xquery/DescendantOrSelfWithNonLocationStepTest.java b/exist-core/src/test/java/org/exist/xquery/DescendantOrSelfWithNonLocationStepTest.java
new file mode 100644
index 00000000000..ec3803e2695
--- /dev/null
+++ b/exist-core/src/test/java/org/exist/xquery/DescendantOrSelfWithNonLocationStepTest.java
@@ -0,0 +1,100 @@
+/*
+ * eXist-db Open Source Native XML Database
+ * Copyright (C) 2001 The eXist-db Authors
+ *
+ * info@exist-db.org
+ * http://www.exist-db.org
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+package org.exist.xquery;
+
+import org.exist.test.ExistXmldbEmbeddedServer;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.xmldb.api.base.ResourceSet;
+import org.xmldb.api.base.XMLDBException;
+import org.xmldb.api.modules.XQueryService;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Tests for // (descendant-or-self) with non-LocationStep expressions.
+ *
+ * The XPath abbreviation // expands to /descendant-or-self::node()/. When
+ * the right-hand side is a LocationStep, the tree walker can merge the axis.
+ * When it is a non-LocationStep expression (parenthesized expression, variable
+ * reference, filtered expression), we must insert an explicit
+ * descendant-or-self::node() step instead.
+ */
+public class DescendantOrSelfWithNonLocationStepTest {
+
+    @ClassRule
+    public static final ExistXmldbEmbeddedServer existEmbeddedServer =
+            new ExistXmldbEmbeddedServer(false, true, true);
+
+    private ResourceSet execute(final String xquery) throws XMLDBException {
+        final XQueryService xqs = existEmbeddedServer.getRoot().getService(XQueryService.class);
+        return xqs.query(xquery);
+    }
+
+    @Test
+    public void parenthesizedAttribute() throws XMLDBException {
+        // //(@x) should find all @x attributes at any depth
+        final ResourceSet result = execute(
+                "let $doc := <root x='1'><a x='2'><b x='3'/></a></root>\n" +
+                "return count($doc//(@x))");
+        assertEquals("3", result.getResource(0).getContent().toString());
+    }
+
+    @Test
+    public void parenthesizedAttributeUnion() throws XMLDBException {
+        // //(@x | @y) should find all @x and @y attributes at any depth
+        final ResourceSet result = execute(
+                "let $doc := <root x='1' y='a'><a x='2'><b y='b'/></a></root>\n" +
+                "return count($doc//(@x | @y))");
+        assertEquals("4", result.getResource(0).getContent().toString());
+    }
+
+    @Test
+    public void parenthesizedElementUnion() throws XMLDBException {
+        // //(b | c) should find elements at any depth, including direct children
+        final ResourceSet result = execute(
+                "let $doc := <root><b/><a><c/><b/></a></root>\n" +
+                "return count($doc//(b | c))");
+        assertEquals("3", result.getResource(0).getContent().toString());
+    }
+
+    @Test
+    public void parenthesizedUnionWithFollowingAxis() throws XMLDBException {
+        // //(north | near-south)/preceding-sibling::comment() should work
+        final ResourceSet result = execute(
+                "let $doc :=\n" +
+                "  <far-north>\n" +
+                "    <!-- 1 -->\n" +
+                "    <north mark='1'>\n" +
+                "      <!-- 2 -->\n" +
+                "      <near-north>\n" +
+                "        <!-- 3 -->\n" +
+                "        <center mark='0'/>\n" +
+                "        <!-- 4 -->\n" +
+                "        <near-south/>\n" +
+                "      </near-north>\n" +
+                "    </north>\n" +
+                "  </far-north>\n" +
+                "return count($doc//(north | near-south)/preceding-sibling::comment())");
+        assertEquals("3", result.getResource(0).getContent().toString());
+    }
+}