gdb says that "disassemble /m" is not a valid command

I'm trying to disassemble a C++ function with gdb 6.8.  I've in the 
manual at:

   http://sourceware.org/gdb/current/onlinedocs/gdb_9.html#SEC64

that "disassemble /m" should also print the source line together with 
the assembly dump.  However, when actually trying it out I get:

   (gdb) disassemble /m
   A syntax error in expression, near `/m'.

Is the documentation out of date?  How do I get source and assembly at 
the same time?  "help disassemble" doesn't say anything about "/m" and 
neither the gdb info pages.