diff --git a/hibernate-core/src/main/java/org/hibernate/criterion/NotExpression.java b/hibernate-core/src/main/java/org/hibernate/criterion/NotExpression.java
index 845b739dacfd..35bf4e5346c9 100644
--- a/hibernate-core/src/main/java/org/hibernate/criterion/NotExpression.java
+++ b/hibernate-core/src/main/java/org/hibernate/criterion/NotExpression.java
@@ -25,12 +25,12 @@
 package org.hibernate.criterion;
 import org.hibernate.Criteria;
 import org.hibernate.HibernateException;
-import org.hibernate.dialect.MySQLDialect;
 import org.hibernate.engine.spi.TypedValue;
 
 /**
  * Negates another criterion
  * @author Gavin King
+ * @author Brett Meyer
  */
 public class NotExpression implements Criterion {
 
@@ -40,14 +40,9 @@ protected NotExpression(Criterion criterion) {
 		this.criterion = criterion;
 	}
 
-	public String toSqlString(Criteria criteria, CriteriaQuery criteriaQuery)
-	throws HibernateException {
-		if ( criteriaQuery.getFactory().getDialect() instanceof MySQLDialect ) {
-			return "not (" + criterion.toSqlString(criteria, criteriaQuery) + ')';
-		}
-		else {
-			return "not " + criterion.toSqlString(criteria, criteriaQuery);
-		}
+	public String toSqlString(Criteria criteria, CriteriaQuery criteriaQuery) throws HibernateException {
+		return criteriaQuery.getFactory().getDialect().getNotExpression(
+				criterion.toSqlString( criteria, criteriaQuery ) );
 	}
 
 	public TypedValue[] getTypedValues(
diff --git a/hibernate-core/src/main/java/org/hibernate/dialect/Dialect.java b/hibernate-core/src/main/java/org/hibernate/dialect/Dialect.java
index f7c417549ac0..4faac80150a9 100644
--- a/hibernate-core/src/main/java/org/hibernate/dialect/Dialect.java
+++ b/hibernate-core/src/main/java/org/hibernate/dialect/Dialect.java
@@ -2311,4 +2311,8 @@ public boolean useFollowOnLocking() {
 	public UniqueDelegate getUniqueDelegate() {
 		return uniqueDelegate;
 	}
+	
+	public String getNotExpression( String expression ) {
+		return "not " + expression;
+	}
 }
diff --git a/hibernate-core/src/main/java/org/hibernate/dialect/MySQLDialect.java b/hibernate-core/src/main/java/org/hibernate/dialect/MySQLDialect.java
index ac33edf5b058..62f8b2479ffc 100644
--- a/hibernate-core/src/main/java/org/hibernate/dialect/MySQLDialect.java
+++ b/hibernate-core/src/main/java/org/hibernate/dialect/MySQLDialect.java
@@ -396,4 +396,9 @@ public JDBCException convert(SQLException sqlException, String message, String s
 			}
 		};
 	}
+	
+	@Override
+	public String getNotExpression( String expression ) {
+		return "not (" + expression + ")";
+	}
 }
diff --git a/hibernate-core/src/main/java/org/hibernate/dialect/Oracle8iDialect.java b/hibernate-core/src/main/java/org/hibernate/dialect/Oracle8iDialect.java
index faa634c6377b..123e38e24977 100644
--- a/hibernate-core/src/main/java/org/hibernate/dialect/Oracle8iDialect.java
+++ b/hibernate-core/src/main/java/org/hibernate/dialect/Oracle8iDialect.java
@@ -581,4 +581,9 @@ public boolean forceLobAsLastValue() {
 	public boolean useFollowOnLocking() {
 		return true;
 	}
+	
+	@Override
+	public String getNotExpression( String expression ) {
+		return "not (" + expression + ")";
+	}
 }
diff --git a/hibernate-core/src/main/java/org/hibernate/dialect/Oracle9Dialect.java b/hibernate-core/src/main/java/org/hibernate/dialect/Oracle9Dialect.java
index d0f0d8ce7943..22c11f6e0196 100644
--- a/hibernate-core/src/main/java/org/hibernate/dialect/Oracle9Dialect.java
+++ b/hibernate-core/src/main/java/org/hibernate/dialect/Oracle9Dialect.java
@@ -377,4 +377,9 @@ public boolean supportsExistsInSelect() {
 	public int getInExpressionCountLimit() {
 		return PARAM_LIST_SIZE_LIMIT;
 	}
+	
+	@Override
+	public String getNotExpression( String expression ) {
+		return "not (" + expression + ")";
+	}
 }
diff --git a/hibernate-core/src/test/java/org/hibernate/test/criteria/CriteriaQueryTest.java b/hibernate-core/src/test/java/org/hibernate/test/criteria/CriteriaQueryTest.java
index 03ba24a86fc9..d20158d13027 100755
--- a/hibernate-core/src/test/java/org/hibernate/test/criteria/CriteriaQueryTest.java
+++ b/hibernate-core/src/test/java/org/hibernate/test/criteria/CriteriaQueryTest.java
@@ -2011,6 +2011,41 @@ public void testCriteriaFetchMode() {
 		session.close();
 		
 	}
+        
+    @Test
+    @TestForIssue( jiraKey = "HHH-6643" )
+    public void testNotNot() {
+    	Student student1 = new Student();
+    	student1.setName("Foo1 Foo1");
+    	student1.setStudentNumber(1);
+    	Student student2 = new Student();
+    	student2.setName("Foo2 Foo2");
+    	student2.setStudentNumber(2);
+    	
+    	Session s = openSession();
+		Transaction t = s.beginTransaction();
+		
+		s.persist( student1 );
+		s.persist( student2 );
+		s.flush();
+		s.clear();
+		
+		// Although this example is simplified and the "not not" is pointless,
+		// double negatives can occur in some dynamic applications (regardless
+		// if it results from bad design or not).  Test to ensure the dialect
+		// handles them as expected.
+		List<Student> students = s.createCriteria( Student.class ).add(
+				Restrictions.not(
+						Restrictions.not(
+								Restrictions.eq( "studentNumber", 1l ) ) )
+		).list();
+		
+		assertEquals( students.size(), 1 );
+		assertEquals( students.get( 0 ).getStudentNumber(), 1 );
+		
+		t.commit();
+		session.close();
+    }
 
 }