diff --git a/src/NHibernate.Test/Async/NHSpecificTest/GH3327/Fixture.cs b/src/NHibernate.Test/Async/NHSpecificTest/GH3327/Fixture.cs
new file mode 100644
index 00000000000..b34a71f1317
--- /dev/null
+++ b/src/NHibernate.Test/Async/NHSpecificTest/GH3327/Fixture.cs
@@ -0,0 +1,63 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by AsyncGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH3327
+{
+	using System.Threading.Tasks;
+	[TestFixture]
+	public class FixtureAsync : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using var session = OpenSession();
+			using var t = session.BeginTransaction();
+			var parent = new Entity { Name = "Parent" };
+			var child = new ChildEntity { Name = "Child", Parent = parent };
+			session.Save(parent);
+			session.Save(child);
+			t.Commit();
+		}
+
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+			session.CreateQuery("delete from ChildEntity").ExecuteUpdate();
+			session.CreateQuery("delete from Entity").ExecuteUpdate();
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public async Task NotIsCorrectlyHandledAsync()
+		{
+			using var session = OpenSession();
+			var q = session.CreateQuery(
+				@"SELECT COUNT(ROOT.Id)
+					FROM Entity AS ROOT
+					WHERE (
+						EXISTS (FROM ChildEntity AS CHILD WHERE CHILD.Parent = ROOT)
+						AND ROOT.Name = 'Parent'
+					)");
+			Assert.That((await (q.ListAsync()))[0], Is.EqualTo(1));
+
+			q = session.CreateQuery(
+				@"SELECT COUNT(ROOT.Id)
+					FROM Entity AS ROOT
+					WHERE NOT (
+						EXISTS (FROM ChildEntity AS CHILD WHERE CHILD.Parent = ROOT)
+						AND ROOT.Name = 'Parent'
+					)");
+			Assert.That((await (q.ListAsync()))[0], Is.EqualTo(0));
+		}
+	}
+}
diff --git a/src/NHibernate.Test/NHSpecificTest/GH3327/Entity.cs b/src/NHibernate.Test/NHSpecificTest/GH3327/Entity.cs
new file mode 100644
index 00000000000..9f9b2bafce2
--- /dev/null
+++ b/src/NHibernate.Test/NHSpecificTest/GH3327/Entity.cs
@@ -0,0 +1,17 @@
+using System;
+
+namespace NHibernate.Test.NHSpecificTest.GH3327
+{
+	public class Entity
+	{
+		public virtual int Id { get; set; }
+ 		public virtual string Name { get; set; }
+	}
+
+	public class ChildEntity
+	{
+		public virtual int Id { get; set; }
+		public virtual Entity Parent { get; set; }
+		public virtual string Name { get; set; }
+	}
+}
diff --git a/src/NHibernate.Test/NHSpecificTest/GH3327/Fixture.cs b/src/NHibernate.Test/NHSpecificTest/GH3327/Fixture.cs
new file mode 100644
index 00000000000..aef1a40243e
--- /dev/null
+++ b/src/NHibernate.Test/NHSpecificTest/GH3327/Fixture.cs
@@ -0,0 +1,52 @@
+using NUnit.Framework;
+
+namespace NHibernate.Test.NHSpecificTest.GH3327
+{
+	[TestFixture]
+	public class Fixture : BugTestCase
+	{
+		protected override void OnSetUp()
+		{
+			using var session = OpenSession();
+			using var t = session.BeginTransaction();
+			var parent = new Entity { Name = "Parent" };
+			var child = new ChildEntity { Name = "Child", Parent = parent };
+			session.Save(parent);
+			session.Save(child);
+			t.Commit();
+		}
+
+		protected override void OnTearDown()
+		{
+			using var session = OpenSession();
+			using var transaction = session.BeginTransaction();
+			session.CreateQuery("delete from ChildEntity").ExecuteUpdate();
+			session.CreateQuery("delete from Entity").ExecuteUpdate();
+
+			transaction.Commit();
+		}
+
+		[Test]
+		public void NotIsCorrectlyHandled()
+		{
+			using var session = OpenSession();
+			var q = session.CreateQuery(
+				@"SELECT COUNT(ROOT.Id)
+					FROM Entity AS ROOT
+					WHERE (
+						EXISTS (FROM ChildEntity AS CHILD WHERE CHILD.Parent = ROOT)
+						AND ROOT.Name = 'Parent'
+					)");
+			Assert.That(q.List()[0], Is.EqualTo(1));
+
+			q = session.CreateQuery(
+				@"SELECT COUNT(ROOT.Id)
+					FROM Entity AS ROOT
+					WHERE NOT (
+						EXISTS (FROM ChildEntity AS CHILD WHERE CHILD.Parent = ROOT)
+						AND ROOT.Name = 'Parent'
+					)");
+			Assert.That(q.List()[0], Is.EqualTo(0));
+		}
+	}
+}
diff --git a/src/NHibernate.Test/NHSpecificTest/GH3327/Mappings.hbm.xml b/src/NHibernate.Test/NHSpecificTest/GH3327/Mappings.hbm.xml
new file mode 100644
index 00000000000..a6eee729fae
--- /dev/null
+++ b/src/NHibernate.Test/NHSpecificTest/GH3327/Mappings.hbm.xml
@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHibernate.Test"
+                   namespace="NHibernate.Test.NHSpecificTest.GH3327">
+
+  <class name="Entity">
+    <id name="Id" generator="identity" />
+    <property name="Name"/>
+  </class>
+
+  <class name="ChildEntity">
+    <id name="Id" generator="identity" />
+    <many-to-one name="Parent" class="Entity" not-null="true" />
+    <property name="Name"/>
+  </class>
+
+</hibernate-mapping>
diff --git a/src/NHibernate/Hql/Ast/ANTLR/HqlParser.cs b/src/NHibernate/Hql/Ast/ANTLR/HqlParser.cs
index f33f8b13acb..6c05fc6c999 100644
--- a/src/NHibernate/Hql/Ast/ANTLR/HqlParser.cs
+++ b/src/NHibernate/Hql/Ast/ANTLR/HqlParser.cs
@@ -214,14 +214,14 @@ public IASTNode NegateNode(IASTNode node)
 				case OR:
 					node.Type = AND;
 					node.Text = "{and}";
-					NegateNode(node.GetChild(0));
-					NegateNode(node.GetChild(1));
+					node.SetChild(0, NegateNode(node.GetChild(0)));
+					node.SetChild(1, NegateNode(node.GetChild(1)));
 					return node;
 				case AND:
 					node.Type = OR;
 					node.Text = "{or}";
-					NegateNode(node.GetChild(0));
-					NegateNode(node.GetChild(1));
+					node.SetChild(0, NegateNode(node.GetChild(0)));
+					node.SetChild(1, NegateNode(node.GetChild(1)));
 					return node;
 				case EQ:
 					node.Type = NE;