diff --git a/configure.ac b/configure.ac
index 56325f7..b36f097 100644
--- a/configure.ac
+++ b/configure.ac
@@ -204,6 +204,23 @@ AM_CONDITIONAL(HAVE_RC, [test -n "[$]_LT_TAGVAR(compiler, RC)"])
 ## ------------- ##
 AM_MISSING_PROG([HELP2MAN], [help2man])
 
+## -------------- ##
+## Darwin warning ##
+## -------------- ##
+
+_warn_darwin="$prefix,$program_transform_name$host_os"
+case "$_warn_darwin" in
+	/usr,s,x,x,darwin*)
+	AC_MSG_WARN([Configuring with --prefix=/usr and no transform name]
+		    [on darwin is not recommended. If installed, it will]
+		    [overwrite /usr/bin/libtool, which is a vendor]
+		    [supplied binary with different functionality.]
+		    [Either reconfigure with a different prefix, or]
+		    [perhaps with --program-prefix=g])
+	;;
+	*) ;;
+esac
+
 ## -------- ##
 ## Outputs. ##
 ## -------- ##