--- a/makefile.in
+++ b/makefile.in
@@ -49,8 +49,8 @@ config.h: makefile VERSION mkconfig.sh # and actually picosat.c
 	rm -f $@; ./mkconfig.sh > $@
 
 libpicosat.a: picosat.o version.o
-	ar rc $@ picosat.o version.o
-	ranlib $@
+	$(AR) rc $@ picosat.o version.o
+	$(RANLIB) $@
 
 SONAME=-Xlinker -soname -Xlinker libpicosat.so
 libpicosat.so: picosat.o version.o