iconv installation error (no intern.h file)

Hi I tried to isntall iconv gem but I'm getting this error:
/usr/local/rvm/rubies/ruby-1.9.2-p180/include/ruby-1.9.1/ruby/backward/
st.h:2:2: warning: #warning use "ruby/st.h" instead of bare "st.h"
iconv.c:22:20: error: intern.h: No such file or directory
iconv.c: In function 'map_charset':
iconv.c:139: error: 'struct RHash' has no member named 'tbl'
iconv.c:139: error: 'struct RHash' has no member named 'tbl'
iconv.c:142: error: 'struct RHash' has no member named 'tbl'
iconv.c: In function 'iconv_create':
iconv.c:187: error: 'struct RString' has no member named 'len'
iconv.c:188: error: 'struct RString' has no member named 'len'
iconv.c:190: error: 'struct RString' has no member named 'ptr'
iconv.c:191: error: 'struct RString' has no member named 'ptr'
iconv.c:191: error: 'struct RString' has no member named 'ptr'
iconv.c:192: error: 'struct RString' has no member named 'ptr'
iconv.c:193: error: 'struct RString' has no member named 'len'
iconv.c: In function 'iconv_fail':
iconv.c:328: error: 'struct RString' has no member named 'len'
iconv.c: In function 'iconv_fail_retry':
iconv.c:352: error: 'ruby_errinfo' undeclared (first use in this
function)
iconv.c:352: error: (Each undeclared identifier is reported only once
iconv.c:352: error: for each function it appears in.)
iconv.c: In function 'rb_str_derive':
iconv.c:371: error: 'struct RString' has no member named 'ptr'
iconv.c:371: error: 'struct RString' has no member named 'len'
iconv.c:373: error: 'struct RString' has no member named 'ptr'
iconv.c:373: error: 'struct RString' has no member named 'len'
iconv.c:374: error: 'struct RString' has no member named 'ptr'
iconv.c: In function 'iconv_convert':
iconv.c:418: error: 'struct RArray' has no member named 'len'
iconv.c:418: error: 'struct RArray' has no member named 'ptr'
iconv.c:436: error: 'struct RString' has no member named 'len'
iconv.c:437: error: 'struct RString' has no member named 'ptr'
iconv.c:455: warning: comparison of unsigned expression >= 0 is always
true
iconv.c:458: warning: comparison between signed and unsigned
iconv.c:459: warning: comparison between signed and unsigned
iconv.c:497: error: 'struct RArray' has no member named 'len'
iconv.c:498: error: 'struct RArray' has no member named 'ptr'
iconv.c:499: error: 'struct RArray' has no member named 'ptr'
iconv.c:501: error: 'struct RString' has no member named 'len'
iconv.c:502: error: 'struct RString' has no member named 'ptr'
iconv.c: In function 'iconv_s_convert':
iconv.c:615: error: 'struct RString' has no member named 'len'
*** Error code 1

I have freeBSD 8.2 and ruby installed by RVM.