diff --git a/cf/krb-find-db.m4 b/cf/krb-find-db.m4
index 84225260d..8b8657141 100644
--- a/cf/krb-find-db.m4
+++ b/cf/krb-find-db.m4
@@ -58,10 +58,11 @@ int main()
 done
 
 AC_MSG_CHECKING(for NDBM library)
+ac_ndbm=no
 if test "$lib_db" != no; then
 	LIB_DBM="$lib_db"
-	AC_DEFINE(NDBM)dnl
-	AC_DEFINE(HAVE_NEW_DB)
+	ac_ndbm=yes
+	AC_DEFINE(HAVE_NEW_DB, 1, [Define if NDBM really is DB (creates files ending in .db).])
 	if test "$LIB_DBM"; then
 		ac_res="yes, $LIB_DBM"
 	else
@@ -69,7 +70,7 @@ if test "$lib_db" != no; then
 	fi
 elif test "$lib_dbm" != no; then
 	LIB_DBM="$lib_dbm"
-	AC_DEFINE(NDBM)dnl
+	ac_ndbm=yes
 	if test "$LIB_DBM"; then
 		ac_res="yes, $LIB_DBM"
 	else
@@ -79,6 +80,7 @@ else
 	LIB_DBM=""
 	ac_res=no
 fi
+test "$ac_ndbm" = yes && AC_DEFINE(NDBM, 1, [Define if you have NDBM (and not DBM)])dnl
 AC_SUBST(LIB_DBM)
 AC_MSG_RESULT($ac_res)
 
diff --git a/cf/krb-func-getcwd-broken.m4 b/cf/krb-func-getcwd-broken.m4
index 51b709cfb..a3a46cdfa 100644
--- a/cf/krb-func-getcwd-broken.m4
+++ b/cf/krb-func-getcwd-broken.m4
@@ -31,7 +31,7 @@ int main()
 ], ac_cv_func_getcwd_broken=yes,:,:)
 ])
 if test "$ac_cv_func_getcwd_broken" = yes; then
-	AC_DEFINE(BROKEN_GETCWD, 1)dnl
+	AC_DEFINE(BROKEN_GETCWD, 1, [Define if getcwd is broken (like in SunOS 4).])dnl
 	LIBOBJS="$LIBOBJS getcwd.o"
 	AC_SUBST(LIBOBJS)dnl
 	AC_MSG_RESULT($ac_cv_func_getcwd_broken)