diff --git a/cdm/src/main/java/ucar/nc2/NetcdfFileWriter.java b/cdm/src/main/java/ucar/nc2/NetcdfFileWriter.java
index <HASH>..<HASH> 100644
--- a/cdm/src/main/java/ucar/nc2/NetcdfFileWriter.java
+++ b/cdm/src/main/java/ucar/nc2/NetcdfFileWriter.java
@@ -469,7 +469,7 @@ public class NetcdfFileWriter {
 

     shortName = makeValidObjectName(shortName);

     if (!isValidDataType(dataType))

-      throw new IllegalArgumentException("illegal dataType: "+dataType);

+      throw new IllegalArgumentException("illegal dataType: "+dataType+" not supported in netcdf-3");

 

     // check unlimited if netcdf-3

     if (!version.isNetdf4format()) {
made nicer error message when illegal datatypes encountered trying to write netcdf-3