diff --git a/src/backend/lib/stringinfo.c b/src/backend/lib/stringinfo.c
index 1745f0f9ca139274fee392b2dabeccf4d8a8056f..544ae1b3a205d0dfd322ba382441e9d74fa6d5e4 100644
--- a/src/backend/lib/stringinfo.c
+++ b/src/backend/lib/stringinfo.c
@@ -9,7 +9,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	  $Id: stringinfo.c,v 1.29 2001/10/25 05:49:29 momjian Exp $
+ *	  $Id: stringinfo.c,v 1.30 2002/03/04 18:34:02 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -114,11 +114,22 @@ appendStringInfo(StringInfo str, const char *fmt,...)
 		avail = str->maxlen - str->len - 1;
 		if (avail > 16)
 		{
+			/*
+			 * Assert check here is to catch buggy vsnprintf that overruns
+			 * the specified buffer length.  Solaris 7 in 64-bit mode is
+			 * an example of a platform with such a bug.
+			 */
+#ifdef USE_ASSERT_CHECKING
+			str->data[str->maxlen-1] = '\0';
+#endif
+
 			va_start(args, fmt);
 			nprinted = vsnprintf(str->data + str->len, avail,
 								 fmt, args);
 			va_end(args);
 
+			Assert(str->data[str->maxlen-1] == '\0');
+
 			/*
 			 * Note: some versions of vsnprintf return the number of chars
 			 * actually stored, but at least one returns -1 on failure. Be