How can I write colons in constant document for rdoc?

I tried to write a document for DBM::VERSION:

| % tail -15 ext/dbm/dbm.c
|         /*
|          * Identifies ndbm library version.
|          *
|          * Examples:
|          *
|          * - "ndbm (4.3BSD)"
|          * - "Berkeley DB 4.8.30: (April  9, 2010)"
|          * - "Berkeley DB (unknown)" (4.4BSD, maybe)
|          * - "GDBM version 1.8.3. 10/15/2002 (built Jul  1 2011 12:32:45)"
|          * - "QDBM 1.8.78"
|          *
|          */
|         rb_define_const(rb_cDBM, "VERSION", version);
|     }
| }
| % rm -rf d
| % rdoc --op d ext/dbm/dbm.c
| Parsing sources...
| 100% [ 1/ 1]  ext/dbm/dbm.c
|
| Generating Darkfish format into /home/ruby/tcstate/ruby/d...
|
| Files:       1
|
| Classes:     2 (0 undocumented)
| Modules:     0 (0 undocumented)
| Constants:   5 (0 undocumented)
| Attributes:  0 (0 undocumented)
| Methods:    37 (0 undocumented)
|
| Total:      44 (0 undocumented)
| 100.00% documented
|
| Elapsed: 0.4s

But rdoc seems to ignore most of the comment
to generate d/DBM.html.

| % w3m -O US-ASCII -dump d/DBM.html
| (snip)
| VERSION
|
|     45)?
|
|       + ?QDBM 1.8.78?
| (snip)

I couldn't find a way to write the document, sigh.
-- 
Tanaka Akira