https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63217
--- Comment #2 from Edward <vz at quantitativesystems dot com> --- I can confirm the bug in version 6.3.0 freshly built: (found this bug researching for a similar bug I am reporting) Using built-in specs. COLLECT_GCC=/home/h/packages/gcc-6.3.0/bin/g++ COLLECT_LTO_WRAPPER=/home/h/packages/gcc-6.3.0/libexec/gcc/x86_64-pc-linux-gnu/6.3.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../gcc-6.3.0/configure --prefix=/home/h/packages/gcc-6.3.0 --enable-languages=c++ Thread model: posix gcc version 6.3.0 (GCC) COLLECT_GCC_OPTIONS='-v' '-std=c++1z' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /home/h/packages/gcc-6.3.0/libexec/gcc/x86_64-pc-linux-gnu/6.3.0/cc1plus -quiet -v -D_GNU_SOURCE src/f5.cpp -quiet -dumpbase f5.cpp -mtune=generic -march=x86-64 -auxbase f5 -std=c++1z -version -o /tmp/ccSkJoqY.s GNU C++14 (GCC) version 6.3.0 (x86_64-pc-linux-gnu) compiled by GNU C version 6.3.0, GMP version 5.1.1, MPFR version 3.1.1, MPC version 1.0.1, isl version none GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 ignoring nonexistent directory "/home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/../../../../x86_64-pc-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/../../../../include/c++/6.3.0 /home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/../../../../include/c++/6.3.0/x86_64-pc-linux-gnu /home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward /home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/include /usr/local/include /home/h/packages/gcc-6.3.0/include /home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/include-fixed /usr/include End of search list. GNU C++14 (GCC) version 6.3.0 (x86_64-pc-linux-gnu) compiled by GNU C version 6.3.0, GMP version 5.1.1, MPFR version 3.1.1, MPC version 1.0.1, isl version none GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 80f12065068033b5f76b36dba8781986 src/f5.cpp: In function ‘int main()’: src/f5.cpp:8:18: error: cannot convert ‘foo’ to ‘int’ in initialization int t((foo()));