diff --git a/src/configure.ac b/src/configure.ac
index cfc3b1b..107c170 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -3709,7 +3709,7 @@
 	getpgid setpgid setsid sigaltstack sigstack sigset sigsetjmp sigaction \
 	sigprocmask sigvec strcasecmp strerror strftime stricmp strncasecmp \
 	strnicmp strpbrk strtol tgetent towlower towupper iswupper \
-	usleep utime utimes mblen ftruncate)
+	usleep utime utimes mblen ftruncate unsetenv)
 AC_FUNC_FSEEKO
 
 dnl define _LARGE_FILES, _FILE_OFFSET_BITS and _LARGEFILE_SOURCE when