When compiling the Boost source tree (Aug 22, 2006 snapshot) with GCC 3.4 on Gentoo Linux on AMD64, you¹ll get 3 warnings about unused variables. The patch is attached. Building: bjam -sTOOLS=gcc -s"GCC=gcc -Wall -Werror" -s"GXX=g++ -Wall -Werror" -q stage Compiler: gcc (GCC) 3.4.4 (Gentoo 3.4.4-r1, ssp-3.4.4-1.0, pie-8.7.8) Copyright (C) 2004 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. Uname: Linux ses0247 2.6.15-gentoo-r5-1 #2 SMP Fri Mar 10 17:11:28 UTC 2006 x86_64 Dual Core AMD Opteron(tm) Processor 275 AuthenticAMD GNU/Linux The 3 variables concerned are created to be used in an assert() statement, but any asserts get replaced with static_cast<void>(0), thus resulting in an unused variable. Breaking up declaration and initialization fixes this issue.