--- a/Makefile	Wed Nov 17 15:55:51 2010 +0100
+++ b/Makefile	Wed Nov 17 18:29:21 2010 +0100
@@ -65,8 +65,25 @@
     sort | \
     $(SED) 's,^[^ ]* ,,'
 
+CHECK_PROG = \
+    @[ -x "`which $(1) 2>&1`" ] || ( echo "$(1) is not installed or not in the path"; exit 128; )
+
 .PHONY: all
-all: $(PKGS)
+all: check $(PKGS)
+
+.PHONY: check
+check:
+	$(call CHECK_PROG,wget)
+	$(call CHECK_PROG,openssl)
+	$(call CHECK_PROG,grep)
+	$(call CHECK_PROG,gzip)
+	$(call CHECK_PROG,tar)
+	$(call CHECK_PROG,xz)
+	$(call CHECK_PROG,unzip)
+	$(call CHECK_PROG,$(SED))
+	$(call CHECK_PROG,$(PATCH))
+	$(call CHECK_PROG,$(INSTALL))
+	$(call CHECK_PROG,$(LIBTOOLIZE))
 
 .PHONY: download
 download: $(addprefix download-,$(PKGS))