--- a/stage4/generate_c/generate_c.cc	Thu Oct 04 14:30:51 2012 +0100
+++ b/stage4/generate_c/generate_c.cc	Thu Oct 04 15:10:45 2012 +0100
@@ -352,12 +352,13 @@
   interval_c *interval = dynamic_cast<interval_c *>(symbol);
   duration_c *duration = dynamic_cast<duration_c *>(symbol);
   
-  if ((NULL == interval) && (NULL == duration)) ERROR;
+  if ((NULL == interval) && (NULL == duration))
+  	  {STAGE4_ERROR(symbol, symbol, "This type of interval value is not currently supported"); ERROR;}
 
   if (NULL != duration) {
     /* SYM_REF2(duration_c, neg, interval) */
     if (duration->neg != NULL)
-      {STAGE4_ERROR(duration, duration, "Negative TIME literals are not currently supported"); ERROR;}
+      {STAGE4_ERROR(duration, duration, "Negative TIME literals for interval are not currently supported"); ERROR;}
     return calculate_time(duration->interval);
   }