diff --git a/configure b/configure
index 80ca1c9221..9cdce69b78 100755
--- a/configure
+++ b/configure
@@ -4,9 +4,8 @@
 #
 
 # Unset some variables known to interfere with behavior of common tools,
-# just as autoconf does.
-CLICOLOR_FORCE= GREP_OPTIONS=
-unset CLICOLOR_FORCE GREP_OPTIONS
+# just as autoconf does.  Unlike autoconf, we assume that unset exists.
+unset CLICOLOR_FORCE GREP_OPTIONS BASH_ENV ENV MAIL MAILPATH CDPATH
 
 # Don't allow CCACHE, if present, to use cached results of compile tests!
 export CCACHE_RECACHE=yes