--- a/makefile
+++ b/makefile
@@ -11,11 +11,11 @@
 HEADERS = general.h clustalw.h
 
 CC	= cc
-CFLAGS  = -c -O
-LFLAGS	= -O -lm 
+CFLAGS  += -c
+LIBS	= -lm 
 
 clustalw : $(OBJECTS) amenu.o clustalw.o
-	$(CC) -o $@ $(OBJECTS) amenu.o clustalw.o $(LFLAGS)
+	$(CC) $(LDFLAGS) -o $@ $(OBJECTS) amenu.o clustalw.o $(LIBS)
 
 interface.o : interface.c $(HEADERS) param.h
 	$(CC) $(CFLAGS) $*.c