--- a/client.mk
+++ b/client.mk
@@ -90,16 +90,20 @@ ifeq (,$(wildcard client.mk))
 endif
 TOPSRCDIR = $(CWD)
 endif
 
 # try to find autoconf 2.13 - discard errors from 'which'
 # MacOS X 10.4 sends "no autoconf*" errors to stdout, discard those via grep
 AUTOCONF ?= $(shell which autoconf-2.13 autoconf2.13 autoconf213 2>/dev/null | grep -v '^no autoconf' | head -1)
 
+ifeq (,$(strip $(AUTOCONF)))
+$(error Couldn't find autoconf 2.13)
+endif
+
 MKDIR := mkdir
 SH := /bin/sh
 ifndef MAKE
 MAKE := gmake
 endif
 PERL ?= perl
 PYTHON ?= python