diff --git a/src/backend/storage/page/bufpage.c b/src/backend/storage/page/bufpage.c
index 32b80c182f0..ad1c8c3ed3f 100644
--- a/src/backend/storage/page/bufpage.c
+++ b/src/backend/storage/page/bufpage.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.77 2008/01/01 19:45:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.78 2008/02/10 20:39:08 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -489,6 +489,9 @@ PageGetExactFreeSpace(Page page)
 	space = (int) ((PageHeader) page)->pd_upper -
 		(int) ((PageHeader) page)->pd_lower;
 
+	if (space < 0)
+		return 0;
+
 	return (Size) space;
 }