diff --git a/configure b/configure
index d3582f56b8..b28620fbef 100755
--- a/configure
+++ b/configure
@@ -16183,15 +16183,32 @@ case $host_os in
         # Unix sockets.
         mingw*)
 
+$as_echo "#define HAVE_SETENV 1" >>confdefs.h
+
+
 $as_echo "#define HAVE_UNSETENV 1" >>confdefs.h
 
 
 $as_echo "#define HAVE_GETPEEREID 1" >>confdefs.h
 
+                ac_cv_func_setenv=yes
                 ac_cv_func_unsetenv=yes
                 ac_cv_func_getpeereid=yes;;
         *)
-                ac_fn_c_check_func "$LINENO" "unsetenv" "ac_cv_func_unsetenv"
+                ac_fn_c_check_func "$LINENO" "setenv" "ac_cv_func_setenv"
+if test "x$ac_cv_func_setenv" = xyes; then :
+  $as_echo "#define HAVE_SETENV 1" >>confdefs.h
+
+else
+  case " $LIBOBJS " in
+  *" setenv.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS setenv.$ac_objext"
+ ;;
+esac
+
+fi
+
+ac_fn_c_check_func "$LINENO" "unsetenv" "ac_cv_func_unsetenv"
 if test "x$ac_cv_func_unsetenv" = xyes; then :
   $as_echo "#define HAVE_UNSETENV 1" >>confdefs.h
 
diff --git a/configure.in b/configure.in
index bc07e92f8f..2cb6cda654 100644
--- a/configure.in
+++ b/configure.in
@@ -1788,12 +1788,14 @@ case $host_os in
         # and doesn't need a replacement getpeereid because it doesn't use
         # Unix sockets.
         mingw*)
+                AC_DEFINE(HAVE_SETENV, 1, [Define to 1 because replacement version used.])
                 AC_DEFINE(HAVE_UNSETENV, 1, [Define to 1 because replacement version used.])
                 AC_DEFINE(HAVE_GETPEEREID, 1, [Define to 1 because function not required.])
+                ac_cv_func_setenv=yes
                 ac_cv_func_unsetenv=yes
                 ac_cv_func_getpeereid=yes;;
         *)
-                AC_REPLACE_FUNCS([unsetenv getpeereid])
+                AC_REPLACE_FUNCS([setenv unsetenv getpeereid])
 		;;
 esac
 
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 244886a531..9ac86d1c0a 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -495,6 +495,9 @@
 /* Define to 1 if you have the <security/pam_appl.h> header file. */
 #undef HAVE_SECURITY_PAM_APPL_H
 
+/* Define to 1 if you have the `setenv' function. */
+#undef HAVE_SETENV
+
 /* Define to 1 if you have the `setproctitle' function. */
 #undef HAVE_SETPROCTITLE
 
diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32
index 2fc4be5f14..e4590cf2e5 100644
--- a/src/include/pg_config.h.win32
+++ b/src/include/pg_config.h.win32
@@ -371,6 +371,9 @@
 /* Define to 1 if you have the <security/pam_appl.h> header file. */
 /* #undef HAVE_SECURITY_PAM_APPL_H */
 
+/* Define to 1 if you have the `setenv' function. */
+#define HAVE_SETENV 1
+
 /* Define to 1 if you have the `setproctitle' function. */
 /* #undef HAVE_SETPROCTITLE */
 
diff --git a/src/include/port.h b/src/include/port.h
index ebcee1c55c..8a5c6389e6 100644
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -437,6 +437,10 @@ extern size_t strnlen(const char *str, size_t maxlen);
 extern long random(void);
 #endif
 
+#ifndef HAVE_SETENV
+extern int setenv(const char *name, const char *value, int overwrite);
+#endif
+
 #ifndef HAVE_UNSETENV
 extern void unsetenv(const char *name);
 #endif
diff --git a/src/include/port/win32_port.h b/src/include/port/win32_port.h
index f4841fb397..f9daaf66d7 100644
--- a/src/include/port/win32_port.h
+++ b/src/include/port/win32_port.h
@@ -471,6 +471,7 @@ extern void _dosmaperr(unsigned long);
 
 /* in port/win32env.c */
 extern int	pgwin32_putenv(const char *);
+extern int	pgwin32_setenv(const char *name, const char *value, int overwrite);
 extern void pgwin32_unsetenv(const char *);
 
 /* in port/win32security.c */
@@ -481,6 +482,7 @@ extern int	pgwin32_is_admin(void);
 extern BOOL AddUserToTokenDacl(HANDLE hToken);
 
 #define putenv(x) pgwin32_putenv(x)
+#define setenv(x,y,z) pgwin32_setenv(x,y,z)
 #define unsetenv(x) pgwin32_unsetenv(x)
 
 /* Things that exist in MinGW headers, but need to be added to MSVC */
diff --git a/src/port/setenv.c b/src/port/setenv.c
new file mode 100644
index 0000000000..440bc832ce
--- /dev/null
+++ b/src/port/setenv.c
@@ -0,0 +1,48 @@
+/*-------------------------------------------------------------------------
+ *
+ * setenv.c
+ *	  setenv() emulation for machines without it
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/port/setenv.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "c.h"
+
+
+int
+setenv(const char *name, const char *value, int overwrite)
+{
+	char	   *envstr;
+
+	/* Error conditions, per POSIX */
+	if (name == NULL || name[0] == '\0' || strchr(name, '=') != NULL ||
+		value == NULL)
+	{
+		errno = EINVAL;
+		return -1;
+	}
+
+	/* No work if variable exists and we're not to replace it */
+	if (overwrite == 0 && getenv(name) != NULL)
+		return 0;
+
+	/*
+	 * Add or replace the value using putenv().  This will leak memory if the
+	 * same variable is repeatedly redefined, but there's little we can do
+	 * about that when sitting atop putenv().
+	 */
+	envstr = (char *) malloc(strlen(name) + strlen(value) + 2);
+	if (!envstr)				/* not much we can do if no memory */
+		return -1;
+
+	sprintf(envstr, "%s=%s", name, value);
+
+	return putenv(envstr);
+}
diff --git a/src/tools/msvc/Mkvcbuild.pm b/src/tools/msvc/Mkvcbuild.pm
index b13e57fa53..131a4c76c4 100644
--- a/src/tools/msvc/Mkvcbuild.pm
+++ b/src/tools/msvc/Mkvcbuild.pm
@@ -100,7 +100,7 @@ sub mkvcbuild
 	  dirent.c dlopen.c getopt.c getopt_long.c
 	  pread.c pwrite.c pg_bitutils.c
 	  pg_strong_random.c pgcheckdir.c pgmkdirp.c pgsleep.c pgstrcasecmp.c
-	  pqsignal.c mkdtemp.c qsort.c qsort_arg.c quotes.c system.c
+	  pqsignal.c mkdtemp.c qsort.c qsort_arg.c quotes.c setenv.c system.c
 	  sprompt.c strerror.c tar.c thread.c
 	  win32env.c win32error.c win32security.c win32setlocale.c);