--- a/src/goodjava/json/JsonToString.java	Sun Apr 19 20:42:26 2020 -0600
+++ b/src/goodjava/json/JsonToString.java	Tue Apr 21 15:05:39 2020 -0600
@@ -150,7 +150,7 @@
 	private void toString(Map.Entry entry,StringBuilder sb,int indented) throws JsonException {
 		Object key = entry.getKey();
 		if( !(key instanceof String) )
-			throw new JsonException("table keys must be strings");
+			throw new JsonException("table keys must be strings but got "+key.getClass().getSimpleName()+" ("+key+"="+entry.getValue()+")");
 		toString((String)key,sb);
 		sb.append(colon);
 		toString(entry.getValue(),sb,indented);