--- a/makefile.u
+++ b/makefile.u
@@ -82,7 +82,7 @@
 ## of "cc -shared".
 
 libf2c.so: $(OFILES)
-	$(CC) -shared -o libf2c.so $(OFILES)
+	$(CC) -shared $(LDFLAGS) -Wl,-soname,libf2c.so.2 $(OFILES) -o libf2c.so.2 -lm
 
 ### If your system lacks ranlib, you don't need it; see README.