It hangs on chicken 4.10.0 too. And with the -:g and -:d flags, we see this: [debug] resizing heap dynamically from 2097151k to 2097151k ... [GC] (old) fromspace: start=0x00007f07e6cfe010, limit=0x00007f0826cfe008 [GC] (old) tospace: start=0x00007f0866d00010, limit=0x00007f08a6d00008 [GC] resized heap to 2147483632 bytes [GC] (new) fromspace: start=0x00007f0826cff010, limit=0x00007f0866cff008 [GC] (new) tospace: start=0x00007f0866d00010, limit=0x00007f08a6d00008 [debug] resizing heap dynamically from 2097151k to 2097151k ... [GC] (old) fromspace: start=0x00007f0826cff010, limit=0x00007f0866cff008 [GC] (old) tospace: start=0x00007f0866d00010, limit=0x00007f08a6d00008 [GC] resized heap to 2147483632 bytes [GC] (new) fromspace: start=0x00007f07e6cfe010, limit=0x00007f0826cfe008 [GC] (new) tospace: start=0x00007f0866d00010, limit=0x00007f08a6d00008 [debug] resizing heap dynamically from 2097151k to 2097151k ... [GC] (old) fromspace: start=0x00007f07e6cfe010, limit=0x00007f0826cfe008 [GC] (old) tospace: start=0x00007f0866d00010, limit=0x00007f08a6d00008 [GC] resized heap to 2147483632 bytes [GC] (new) fromspace: start=0x00007f0826cff010, limit=0x00007f0866cff008 [GC] (new) tospace: start=0x00007f0866d00010, limit=0x00007f08a6d00008 [debug] resizing heap dynamically from 2097151k to 2097151k ... [GC] (old) fromspace: start=0x00007f0826cff010, limit=0x00007f0866cff008 [GC] (old) tospace: start=0x00007f0866d00010, limit=0x00007f08a6d00008