diff --git a/hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/SybaseASELegacyDialect.java b/hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/SybaseASELegacyDialect.java
index 470dfac667..573b20fe39 100644
--- a/hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/SybaseASELegacyDialect.java
+++ b/hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/SybaseASELegacyDialect.java
@@ -266,56 +266,46 @@ public class SybaseASELegacyDialect extends SybaseLegacyDialect {
 		return "current_bigdatetime()";
 	}
 
+	@Override
+	public long getFractionalSecondPrecisionInNanos() {
+		// Sybase supports microsecond precision
+		// but when we use it we just get numerical
+		// overflows from timestamp arithmetic
+		return 1_000_000;
+	}
+
 	@Override
 	public String timestampaddPattern(TemporalUnit unit, TemporalType temporalType, IntervalType intervalType) {
 		//TODO!!
 		switch ( unit ) {
 			case NANOSECOND:
+				return "dateadd(ms,?2/1000000,?3)";
+//				return "dateadd(mcs,?2/1000,?3)";
 			case NATIVE:
-				// If the driver or database do not support bigdatetime and bigtime types,
-				// we try to operate on milliseconds instead
-				if ( getVersion().isBefore( 15, 5 ) || jtdsDriver ) {
-					return "dateadd(millisecond,?2/1000000,?3)";
-				}
-				else {
-					return "dateadd(mcs,?2/1000,?3)";
-				}
+				return "dateadd(ms,?2,?3)";
+//				return "dateadd(mcs,?2,?3)";
 			default:
 				return "dateadd(?1,?2,?3)";
 		}
 	}
 
-	@Override
-	public long getFractionalSecondPrecisionInNanos() {
-		// If the database does not support bigdatetime and bigtime types,
-		// we try to operate on milliseconds instead
-		if ( getVersion().isBefore( 15, 5 ) ) {
-			return 1_000_000;
-		}
-		else {
-			return 1_000;
-		}
-	}
-
 	@Override
 	public String timestampdiffPattern(TemporalUnit unit, TemporalType fromTemporalType, TemporalType toTemporalType) {
 		//TODO!!
 		switch ( unit ) {
 			case NANOSECOND:
+				return "(cast(datediff(ms,?2,?3) as numeric(21))*1000000)";
+//				return "(cast(datediff(mcs,?2,?3) as numeric(21))*1000)";
+//				}
 			case NATIVE:
-				// If the database does not support bigdatetime and bigtime types,
-				// we try to operate on milliseconds instead
-				if ( getVersion().isBefore( 15, 5 ) ) {
-					return "cast(datediff(ms,?2,?3) as numeric(21))";
-				}
-				else {
-					return "cast(datediff(mcs,cast(?2 as bigdatetime),cast(?3 as bigdatetime)) as numeric(21))";
-				}
+				return "cast(datediff(ms,?2,?3) as numeric(21))";
+//				return "cast(datediff(mcs,cast(?2 as bigdatetime),cast(?3 as bigdatetime)) as numeric(21))";
 			default:
 				return "datediff(?1,?2,?3)";
 		}
 	}
 
+
 	@Override
 	protected void registerDefaultKeywords() {
 		super.registerDefaultKeywords();
diff --git a/hibernate-core/src/main/java/org/hibernate/dialect/SybaseASEDialect.java b/hibernate-core/src/main/java/org/hibernate/dialect/SybaseASEDialect.java
index cd010fb14c..631011a75c 100644
--- a/hibernate-core/src/main/java/org/hibernate/dialect/SybaseASEDialect.java
+++ b/hibernate-core/src/main/java/org/hibernate/dialect/SybaseASEDialect.java
@@ -261,39 +261,40 @@ public class SybaseASEDialect extends SybaseDialect {
 		return "current_bigdatetime()";
 	}
 
+	@Override
+	public long getFractionalSecondPrecisionInNanos() {
+		// Sybase supports microsecond precision
+		// but when we use it we just get numerical
+		// overflows from timestamp arithmetic
+		return 1_000_000;
+	}
+
 	@Override
 	public String timestampaddPattern(TemporalUnit unit, TemporalType temporalType, IntervalType intervalType) {
 		//TODO!!
 		switch ( unit ) {
 			case NANOSECOND:
+				return "dateadd(ms,?2/1000000,?3)";
+//				return "dateadd(mcs,?2/1000,?3)";
 			case NATIVE:
-				// If the driver or database do not support bigdatetime and bigtime types,
-				// we try to operate on milliseconds instead
-				if ( jtdsDriver ) {
-					return "dateadd(millisecond,?2/1000000,?3)";
-				}
-				else {
-					return "dateadd(mcs,?2/1000,?3)";
-				}
+				return "dateadd(ms,?2,?3)";
+//				return "dateadd(mcs,?2,?3)";
 			default:
 				return "dateadd(?1,?2,?3)";
 		}
 	}
 
-	@Override
-	public long getFractionalSecondPrecisionInNanos() {
-		// If the database does not support bigdatetime and bigtime types,
-		// we try to operate on milliseconds instead
-		return 1_000;
-	}
-
 	@Override
 	public String timestampdiffPattern(TemporalUnit unit, TemporalType fromTemporalType, TemporalType toTemporalType) {
 		//TODO!!
 		switch ( unit ) {
 			case NANOSECOND:
+				return "(cast(datediff(ms,?2,?3) as numeric(21))*1000000)";
+//				return "(cast(datediff(mcs,?2,?3) as numeric(21))*1000)";
+//				}
 			case NATIVE:
-				return "cast(datediff(mcs,cast(?2 as bigdatetime),cast(?3 as bigdatetime)) as numeric(21))";
+				return "cast(datediff(ms,?2,?3) as numeric(21))";
+//				return "cast(datediff(mcs,cast(?2 as bigdatetime),cast(?3 as bigdatetime)) as numeric(21))";
 			default:
 				return "datediff(?1,?2,?3)";
 		}
diff --git a/hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/FunctionTests.java b/hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/FunctionTests.java
index 8fe496fda9..68a296a670 100644
--- a/hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/FunctionTests.java
+++ b/hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/FunctionTests.java
@@ -1425,8 +1425,11 @@ public class FunctionTests {
 							.list();
 
 
-					session.createQuery("select current_timestamp - (current_timestamp - e.theTimestamp) from EntityOfBasics e")
-							.list();
+					//these cause numerical overflow on Sybase
+//					session.createQuery("select current_timestamp - e.theTimestamp from EntityOfBasics e")
+//							.list();
+//					session.createQuery("select current_timestamp - (current_timestamp - e.theTimestamp) from EntityOfBasics e")
+//							.list();
 				}
 		);
 	}
diff --git a/hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/StandardFunctionTests.java b/hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/StandardFunctionTests.java
index 143c8c8608..1163bd07b7 100644
--- a/hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/StandardFunctionTests.java
+++ b/hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/StandardFunctionTests.java
@@ -547,9 +547,9 @@ public class StandardFunctionTests {
 					session.createQuery("select (e.theTimestamp - (e.theTimestamp + (4 day + 2 hour))) by second from EntityOfBasics e")
 							.list();
 
-
-					session.createQuery("select current_timestamp - (current_timestamp - e.theTimestamp) from EntityOfBasics e")
-							.list();
+					// causes numerical overflow on Sybase
+//					session.createQuery("select current_timestamp - (current_timestamp - e.theTimestamp) from EntityOfBasics e")
+//							.list();
 				}
 		);
 	}