--- a/Makefile
+++ b/Makefile
@@ -1,10 +1,10 @@
 all: prog_z
 
-prog_z: prog_z.c libmain.so libuseful.so
-	$(CC) $(CFLAGS) $(LDFLAGS) prog_z.c -o prog_z -rdynamic libmain.so libuseful.so -Wl,-rpath,$(shell pwd)
+prog_z: prog_z.c libmain.so
+	$(CC) $(CFLAGS) $(LDFLAGS) prog_z.c -o prog_z -rdynamic libmain.so -Wl,-rpath,$(shell pwd)
 
-libmain.so: main.c main.h useful.h
-	$(CC) -fPIC -shared $(CFLAGS) $(LDFLAGS) main.c -o libmain.so -Wl,-rpath,$(shell pwd)
+libmain.so: main.c main.h useful.h libuseful.so
+	$(CC) -fPIC -shared $(CFLAGS) $(LDFLAGS) main.c -o libmain.so libuseful.so -Wl,-rpath,$(shell pwd)
 
 libuseful.so: useful.c useful.h
 	$(CC) -fPIC -shared $(CFLAGS) $(LDFLAGS) useful.c -o libuseful.so  -Wl,-rpath,$(shell pwd)