subtraction with overflow on i686

[droundy]

I get the following error:

thread 'main' panicked at 'attempt to subtract with overflow', /home/droundy/.cargo/registry/src/github.com-1ecc6299db9ec823/stats_alloc-0.1.8/src/lib.rs:176:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:76
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:60
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1030
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:64
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:196
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:210
  10: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:473
  11: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:380
  12: rust_begin_unwind
             at src/libstd/panicking.rs:307
  13: core::panicking::panic_fmt
             at src/libcore/panicking.rs:85
  14: core::panicking::panic
             at src/libcore/panicking.rs:49
  15: <stats_alloc::Stats as core::ops::arith::SubAssign>::sub_assign
             at /home/droundy/.cargo/registry/src/github.com-1ecc6299db9ec823/stats_alloc-0.1.8/src/lib.rs:176
  16: <stats_alloc::Stats as core::ops::arith::Sub>::sub
             at /home/droundy/.cargo/registry/src/github.com-1ecc6299db9ec823/stats_alloc-0.1.8/src/lib.rs:166
  17: stats_alloc::Region<T>::change
             at /home/droundy/.cargo/registry/src/github.com-1ecc6299db9ec823/stats_alloc-0.1.8/src/lib.rs:211
  18: bench::mem_used
             at benches/bench.rs:15

It looks like the change method is subtracting with overflow.