diff --git a/configure b/configure
index d610e60d630..fc66ce5fac6 100755
--- a/configure
+++ b/configure
@@ -11970,7 +11970,8 @@ fi
 
 
 
-for ac_func in crypt fseeko getopt getrusage inet_aton random rint srandom strcasecmp strdup strerror strtol strtoul
+
+for ac_func in crypt fseeko getopt getrusage inet_aton random rint srandom strcasecmp strdup strerror strtol strtoul unsetenv
 do
 as_ac_var=`echo "ac_cv_func_$ac_func" | $as_tr_sh`
 echo "$as_me:$LINENO: checking for $ac_func" >&5
diff --git a/configure.in b/configure.in
index f0ef9c83afc..a80b8bdb495 100644
--- a/configure.in
+++ b/configure.in
@@ -1,5 +1,5 @@
 dnl Process this file with autoconf to produce a configure script.
-dnl $Header: /cvsroot/pgsql/configure.in,v 1.301.2.16 2005/12/09 20:53:26 tgl Exp $
+dnl $Header: /cvsroot/pgsql/configure.in,v 1.301.2.17 2006/01/05 00:51:25 tgl Exp $
 dnl
 dnl Developers, please strive to achieve this order:
 dnl
@@ -929,7 +929,7 @@ else
   AC_CHECK_FUNCS([fpclass fp_class fp_class_d class], [break])
 fi
 
-AC_REPLACE_FUNCS([crypt fseeko getopt getrusage inet_aton random rint srandom strcasecmp strdup strerror strtol strtoul])
+AC_REPLACE_FUNCS([crypt fseeko getopt getrusage inet_aton random rint srandom strcasecmp strdup strerror strtol strtoul unsetenv])
 
 # system's version of getaddrinfo(), if any, may be used only if we found
 # a definition for struct addrinfo; see notes in src/include/getaddrinfo.h
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 22765878856..5c755038389 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -527,6 +527,9 @@
 /* Define to 1 if you have unix sockets. */
 #undef HAVE_UNIX_SOCKETS
 
+/* Define to 1 if you have the `unsetenv' function. */
+#undef HAVE_UNSETENV
+
 /* Define to 1 if you have the `utime' function. */
 #undef HAVE_UTIME
 
diff --git a/src/include/port.h b/src/include/port.h
index d77dd652f15..15288acfc3b 100644
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: port.h,v 1.14 2003/09/13 14:49:51 momjian Exp $
+ * $Id: port.h,v 1.14.2.1 2006/01/05 00:51:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -105,6 +105,10 @@ extern char *strdup(char const *);
 extern long random(void);
 #endif
 
+#ifndef HAVE_UNSETENV
+extern void unsetenv(const char *name);
+#endif
+
 #ifndef HAVE_SRANDOM
 extern void srandom(unsigned int seed);
 #endif
diff --git a/src/port/unsetenv.c b/src/port/unsetenv.c
new file mode 100644
index 00000000000..36d908fc3ff
--- /dev/null
+++ b/src/port/unsetenv.c
@@ -0,0 +1,56 @@
+/*-------------------------------------------------------------------------
+ *
+ * unsetenv.c
+ *	  unsetenv() emulation for machines without it
+ *
+ * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  $PostgreSQL: pgsql/src/port/unsetenv.c,v 1.6.2.1 2006/01/05 00:51:25 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "c.h"
+
+
+void
+unsetenv(const char *name)
+{
+	char	   *envstr;
+
+	if (getenv(name) == NULL)
+		return;					/* no work */
+
+	/*
+	 * The technique embodied here works if libc follows the Single Unix Spec
+	 * and actually uses the storage passed to putenv() to hold the environ
+	 * entry.  When we clobber the entry in the second step we are ensuring
+	 * that we zap the actual environ member.  However, there are some libc
+	 * implementations (notably recent BSDs) that do not obey SUS but copy the
+	 * presented string.  This method fails on such platforms.	Hopefully all
+	 * such platforms have unsetenv() and thus won't be using this hack.
+	 *
+	 * Note that repeatedly setting and unsetting a var using this code will
+	 * leak memory.
+	 */
+
+	envstr = (char *) malloc(strlen(name) + 2);
+	if (!envstr)				/* not much we can do if no memory */
+		return;
+
+	/* Override the existing setting by forcibly defining the var */
+	sprintf(envstr, "%s=", name);
+	putenv(envstr);
+
+	/* Now we can clobber the variable definition this way: */
+	strcpy(envstr, "=");
+
+	/*
+	 * This last putenv cleans up if we have multiple zero-length names as a
+	 * result of unsetting multiple things.
+	 */
+	putenv(envstr);
+}