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 048ee8e7e85..a4392c13808 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
@@ -2360,7 +2360,13 @@ throws PermissionDeniedException, EXistException, XPathException
                         (s.getTest().getType() == Type.ATTRIBUTE && s.getAxis() == Constants.CHILD_AXIS))
                         // combines descendant-or-self::node()/attribute:*
                         s.setAxis(Constants.DESCENDANT_ATTRIBUTE_AXIS);
-                    else {
+                    else if (s.getAxis() <= Constants.PRECEDING_SIBLING_AXIS) {
+                        // Reverse axis: insert explicit descendant-or-self::node() step
+                        LocationStep descStep = new LocationStep(context, Constants.DESCENDANT_SELF_AXIS, new TypeTest(Type.NODE));
+                        descStep.setAbbreviated(true);
+                        path.replaceLastExpression(descStep);
+                        path.add(step);
+                    } else {
                         s.setAxis(Constants.DESCENDANT_SELF_AXIS);
                         s.setAbbreviated(true);
                     }
@@ -2984,6 +2990,13 @@ throws PermissionDeniedException, EXistException, XPathException
                         rs.setAxis(Constants.DESCENDANT_AXIS);
                     } else if (rs.getAxis() == Constants.SELF_AXIS) {
                         rs.setAxis(Constants.DESCENDANT_SELF_AXIS);
+                    } else if (rs.getAxis() <= Constants.PRECEDING_SIBLING_AXIS) {
+                        // Reverse axis: cannot merge with descendant-or-self,
+                        // insert explicit descendant-or-self::node() step before the reverse axis step
+                        LocationStep descStep = new LocationStep(context, Constants.DESCENDANT_SELF_AXIS, new TypeTest(Type.NODE));
+                        descStep.setAbbreviated(true);
+                        path.replaceLastExpression(descStep);
+                        path.add(rightStep);
                     } else {
                         rs.setAxis(Constants.DESCENDANT_SELF_AXIS);
                         rs.setAbbreviated(true);
diff --git a/exist-core/src/test/java/org/exist/xquery/XPathQueryTest.java b/exist-core/src/test/java/org/exist/xquery/XPathQueryTest.java
index e7fe9b350da..1e035a2ec18 100644
--- a/exist-core/src/test/java/org/exist/xquery/XPathQueryTest.java
+++ b/exist-core/src/test/java/org/exist/xquery/XPathQueryTest.java
@@ -808,6 +808,65 @@ public void precedingAxis() throws XMLDBException {
         queryResource(service, "siblings.xml", "//a/n[. = '3']/preceding::s", 3);
     }
 
+    /**
+     * Tests that // followed by a reverse axis correctly expands to
+     * /descendant-or-self::node()/ + reverse axis, rather than
+     * collapsing the reverse axis into descendant-or-self.
+     *
+     * @see <a href="https://github.com/eXist-db/exist/issues/691">#691</a>
+     */
+    @Test
+    public void dslashWithReverseAxis() throws XMLDBException {
+        final String xml =
+                "<root>" +
+                "   <a>" +
+                "       <b>1</b>" +
+                "       <b>2</b>" +
+                "   </a>" +
+                "   <a>" +
+                "       <b>3</b>" +
+                "       <b>4</b>" +
+                "   </a>" +
+                "</root>";
+
+        final XQueryService service =
+                storeXMLStringAndGetQueryService("dslash_reverse.xml", xml);
+
+        // //preceding::b should produce the same count as the expanded form
+        queryAndAssert(service,
+                "let $d := doc('/db/test/dslash_reverse.xml') " +
+                "return count($d//preceding::b) eq count($d/descendant-or-self::node()/preceding::b)",
+                1, "//preceding::b count should match expanded form");
+
+        // //ancestor::a should produce the same count as the expanded form
+        queryAndAssert(service,
+                "let $d := doc('/db/test/dslash_reverse.xml') " +
+                "return count($d//ancestor::a) eq count($d/descendant-or-self::node()/ancestor::a)",
+                1, "//ancestor::a count should match expanded form");
+
+        // Note: //preceding-sibling::b skipped due to pre-existing NPE in
+        // NewArrayNodeSet.selectPrecedingSiblings when evaluating preceding-sibling
+        // on descendant-or-self::node() context (affects both abbreviated and expanded forms)
+
+        // //ancestor-or-self::a should produce the same count as the expanded form
+        queryAndAssert(service,
+                "let $d := doc('/db/test/dslash_reverse.xml') " +
+                "return count($d//ancestor-or-self::a) eq count($d/descendant-or-self::node()/ancestor-or-self::a)",
+                1, "//ancestor-or-self::a count should match expanded form");
+
+        // //parent::a should produce the same count as the expanded form
+        queryAndAssert(service,
+                "let $d := doc('/db/test/dslash_reverse.xml') " +
+                "return count($d//parent::a) eq count($d/descendant-or-self::node()/parent::a)",
+                1, "//parent::a count should match expanded form");
+
+        // Relative path: $node//preceding::b should match expanded form
+        queryAndAssert(service,
+                "let $node := doc('/db/test/dslash_reverse.xml')/root/a[2] " +
+                "return count($node//preceding::b) eq count($node/descendant-or-self::node()/preceding::b)",
+                1, "$node//preceding::b count should match expanded form");
+    }
+
     @Test
     public void position() throws XMLDBException, IOException, SAXException {