small_vector overflow

Hi guys when I run facebook mvfst and I run the demo tperf I met a problem that client broke out with Internal Error, and finally I
found that this was caused by the function named makeSizeInternal in small_vector.h and it threw exception: max_size exceeded in small_vector. I replace excption code with LOG(INFO) << newSize << " " << max_size() << " " << capacity(); and the result is "32768 32767 32767" every time I run tperf

I wonder why function "emplace_back" in small_vector.h calls "makeSize" with first param being "size() + 1", in light of this I modify the "if" condition "newSize > max_size()" into "newSize > max_size() + 1" in function "makeSizeInternal", it can prevent the overflow, but it is likely to be a improper choice.
So I want to know what kind of method may solve this problem. Thanks!