--- a/client.mk
+++ b/client.mk
@@ -86,17 +86,21 @@ endif
 
 ifndef TOPSRCDIR
 ifeq (,$(wildcard client.mk))
 $(error Must run from the client.mk directory, or specify TOPSRCDIR)
 endif
 TOPSRCDIR = $(CWD)
 endif
 
-AUTOCONF ?= $(shell which autoconf-2.13 autoconf2.13 autoconf213 | head -1)
+ifeq (Darwin,$(shell uname -s))
+AUTOCONF ?= autoconf213
+else
+AUTOCONF ?= autoconf-2.13
+endif
 
 MKDIR := mkdir
 SH := /bin/sh
 ifndef MAKE
 MAKE := gmake
 endif
 PERL ?= perl
 PYTHON ?= python