diff --git a/contrib/pg_freespacemap/pg_freespacemap.c b/contrib/pg_freespacemap/pg_freespacemap.c
index cfe5cb0268c..e4475c1ffc1 100644
--- a/contrib/pg_freespacemap/pg_freespacemap.c
+++ b/contrib/pg_freespacemap/pg_freespacemap.c
@@ -3,7 +3,7 @@
  * pg_freespacemap.c
  *	  display some contents of the free space relation and page maps.
  *
- *	  $PostgreSQL: pgsql/contrib/pg_freespacemap/pg_freespacemap.c,v 1.9 2006/10/19 18:32:46 tgl Exp $
+ *	  $PostgreSQL: pgsql/contrib/pg_freespacemap/pg_freespacemap.c,v 1.9.2.1 2009/04/07 18:11:04 tgl Exp $
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
@@ -94,6 +94,7 @@ pg_freespacemap_pages(PG_FUNCTION_ARGS)
 	if (SRF_IS_FIRSTCALL())
 	{
 		int			i;
+		int			nchunks;	/* Size of freespace.c's arena. */
 		int			numPages;	/* Max possible no. of pages in map. */
 		int			nPages;		/* Mapped pages for a relation. */
 
@@ -102,7 +103,10 @@ pg_freespacemap_pages(PG_FUNCTION_ARGS)
 		 */
 		FreeSpaceMap = GetFreeSpaceMap();
 
-		numPages = MaxFSMPages;
+		/* this must match calculation in InitFreeSpaceMap(): */
+		nchunks = (MaxFSMPages - 1) / CHUNKPAGES + 1;
+		/* Worst case (lots of indexes) could have this many pages: */
+		numPages = nchunks * INDEXCHUNKPAGES;
 
 		funcctx = SRF_FIRSTCALL_INIT();