compile error with Ruby 1.9.1-p376

Hi,
i compile clearsilver with ruby-1.9.1-p376 like:
./configure --with-apache=/usr/local/apache2 --with-python=/usr/bin/python --with-ruby=/usr/bin/ruby --with-ruby-prog=/usr/bin/ruby --with-perl=/usr/bin/perl --disable-csharp --disable-java --enable-gettext

i get the following error message:
make
make[2]: Entering directory `/usr/local/src/AAAnewcompile/clearsilver-0.10.5/ruby/ext/hdf'
gcc -I. -I/usr/include/ruby-1.9.1/i686-linux -I/usr/include/ruby-1.9.1/ruby/backward -I/usr/include/ruby-1.9.1 -I/usr/local/src/AAAnewcompile/clearsilver-0.10.5/ruby/ext/hdf -DHAc
neo_cs.c: In function ‘c_new’:
neo_cs.c:45: error: ‘struct RString’ has no member named ‘ptr’
neo_cs.c:47: error: ‘struct RString’ has no member named ‘ptr’
neo_cs.c: In function ‘c_parse_file’:
neo_cs.c:63: error: ‘struct RString’ has no member named ‘ptr’
neo_cs.c: In function ‘c_parse_str’:
neo_cs.c:84: error: ‘struct RString’ has no member named ‘ptr’
neo_cs.c: In function ‘c_render’:
neo_cs.c:107: error: ‘struct RString’ has no member named ‘ptr’
make[2]: *** [neo_cs.o] Error 1
make[2]: Leaving directory `/usr/local/src/AAAnewcompile/clearsilver-0.10.5/ruby/ext/hdf'
setup failed
'system make' failed
try 'ruby install.rb --help' for usage
make[1]: *** [ext/hdf/hdf.so] Error 1
make[1]: Leaving directory `/usr/local/src/AAAnewcompile/clearsilver-0.10.5/ruby'
make: *** [cs] Error 2

if i disable ruby support i can compile it.
any help would be fine.
(btw. ruby is working)

thx,
tom