Index: lwgeom_geos.c
===================================================================
--- lwgeom_geos.c	(revision 3371)
+++ lwgeom_geos.c	(working copy)
@@ -1025,9 +1025,24 @@
 {
 	int t1 = lwgeom_getType(g1->type);
 	int t2 = lwgeom_getType(g2->type);
+	
+	LWGEOM_UNPARSER_RESULT lwg_unparser_result;
+	int result;
 
-	if (  (t1 == COLLECTIONTYPE) || (t2 == COLLECTIONTYPE) )
-		elog(ERROR,"Relate Operation called with a LWGEOMCOLLECTION type.  This is unsupported");
+	if ( t1 == COLLECTIONTYPE) {
+		result = serialized_lwgeom_to_ewkt(&lwg_unparser_result, SERIALIZED_FORM(g1), PARSER_CHECK_ALL);
+		ereport(ERROR,
+			(errmsg("Relate Operation called with a LWGEOMCOLLECTION type.  This is unsupported"),
+			 errhint("Argument 1: '%s'", lwg_unparser_result.wkoutput))
+		);	
+	}
+	else if (t2 == COLLECTIONTYPE) {
+		result = serialized_lwgeom_to_ewkt(&lwg_unparser_result, SERIALIZED_FORM(g2), PARSER_CHECK_ALL);
+		ereport(ERROR,
+			(errmsg("Relate Operation called with a LWGEOMCOLLECTION type.  This is unsupported"),
+			 errhint("Argument 2: '%s'", lwg_unparser_result.wkoutput))
+		);	
+	}
 }
 
 PG_FUNCTION_INFO_V1(isvalid);
