Error in `./app': free(): invalid next size

[glaslos]

*** Error in `./app': free(): invalid next size (fast): 0x00007f79400b5140 ***

======= Backtrace: =========
/lib64/libc.so.6(+0x7c503)[0x7f7971af5503]
/usr/lib64/libmagic.so.1(file_vprintf+0x6c)[0x7f797247330c]
/usr/lib64/libmagic.so.1(file_printf+0x87)[0x7f79724733e7]
/usr/lib64/libmagic.so.1(file_trycdf+0x4c7)[0x7f7972477157]
/usr/lib64/libmagic.so.1(file_buffer+0x1c6)[0x7f7972473726]
/usr/lib64/libmagic.so.1(magic_buffer+0x31)[0x7f7972467b61]
./app(_cgo_f7c060554b06_Cfunc_magic_buffer+0x1f)[0x8093df]
./app[0x459c60]

I'm using magicmime with multiple goroutines but with a mutex around magicmime.TypeByBuffer(blob)