I just found that the intel compiler (icc 9.0) also supports compiler warnings for portability problems. For the file #include int foo(size_t x) { return x; } it says (with -Wall) a.c(3): remark #1418: external definition with no prior declaration int foo(size_t x) ^ a.c(5): remark #1682: implicit conversion of a 64-bit integral type to a smaller integral type (potential portability problem) return x; ^ If you just want the latter warning, pass -Wp64. Regards, Martin P.S. In case you want to install it on a Debian AMD64 system, here is the procedure: 1. register at https://registrationcenter.intel.com/EvalCenter/EvalForm.aspx?ProductID=408 2. download and unpack the l_cc_c_9.0.030 tarfile. 3. don't try alien, it won't work. 4. don't try the Intel install.sh, it won't work (atleast, it didn't work for me) 5. Instead, install with 'rpm -i --nodeps *.em64t.rpm' 6. edit /opt/intel/cce/9.0/bin/icc, replacing all occurrences of <INSTALLDIR> with /opt/intel/cce/9.0 7. Put the *.lic file that Intel sent you into /opt/intel/cce/9.0/bin