Unhandled addressing mode issue

[ImanHosseini]

While lifting this function:

0000000000015350 <camlStdlib__output_string_245>:
   15350:	48 83 ec 08          	sub    $0x8,%rsp
   15354:	48 8b 7b f8          	mov    -0x8(%rbx),%rdi
   15358:	48 c1 ef 0a          	shr    $0xa,%rdi
   1535c:	48 8d 3c fd ff ff ff 	lea    -0x1(,%rdi,8),%rdi
   15363:	ff 
   15364:	48 0f b6 34 3b       	movzbq (%rbx,%rdi,1),%rsi
   15369:	48 29 f7             	sub    %rsi,%rdi
   1536c:	48 8d 4c 3f 01       	lea    0x1(%rdi,%rdi,1),%rcx
   15371:	ba 01 00 00 00       	mov    $0x1,%edx
   15376:	48 89 c7             	mov    %rax,%rdi
   15379:	48 89 de             	mov    %rbx,%rsi
   1537c:	48 8d 05 4d ac 00 00 	lea    0xac4d(%rip),%rax        # 1ffd0 <caml_ml_output>
   15383:	e8 a4 a9 01 00       	callq  2fd2c <caml_c_call>
   15388:	4d 8b 3e             	mov    (%r14),%r15
   1538b:	48 83 c4 08          	add    $0x8,%rsp
   1538f:	c3                   	retq   

I get "unhandled addressing mode in memory addr" "expression calculation" error at this instruction (the following is coming from "out()<<MI" for that failing instruction):

$rdi = MOV64rm $rbx, 1, $noreg, -8, $noreg, <0x55e9f25dbf28>

This is supposedly the instruction at 15354: "mov -0x8(%rbx),%rdi"
Any leads on how to "handle" this instruction?