diff --git a/mips.ml b/mips.ml
index 31d8b33..b3f81ba 100644
--- a/mips.ml
+++ b/mips.ml
@@ -44,6 +44,7 @@ type instr =
   | Sb of reg * loc
   | Lb of reg * loc
   | Move of reg * reg
+  | Neg of reg * reg
   | Addi of reg * reg * int
   | Add of reg * reg * reg
   | Mul of reg * reg * reg
@@ -112,24 +113,30 @@ let fmt_loc = function
 ;;
 
 let fmt_instr = function
-  | Label l -> Printf.sprintf "%s:" l
-  | Li (r, i) -> Printf.sprintf "  li %s, %d" (fmt_reg r) i
-  | La (r, a) -> Printf.sprintf "  la %s, %s" (fmt_reg r) (fmt_loc a)
-  | Sw (r, a) -> Printf.sprintf "  sw %s, %s" (fmt_reg r) (fmt_loc a)
-  | Lw (r, a) -> Printf.sprintf "  lw %s, %s" (fmt_reg r) (fmt_loc a)
-  | Sb (r, a) -> Printf.sprintf "  sb %s, %s" (fmt_reg r) (fmt_loc a)
-  | Lb (r, a) -> Printf.sprintf "  lb %s, %s" (fmt_reg r) (fmt_loc a)
-  | Move (rd, rs) -> Printf.sprintf "  move %s, %s" (fmt_reg rd) (fmt_reg rs)
-  | Addi (rd, rs, i) -> Printf.sprintf "  addi %s, %s, %d" (fmt_reg rd) (fmt_reg rs) i
-  | Add (rd, rs, rt) ->
-    Printf.sprintf "  add %s, %s, %s" (fmt_reg rd) (fmt_reg rs) (fmt_reg rt)
-  | Mul (rd, rs, rt) ->
-    Printf.sprintf "  mul %s, %s, %s" (fmt_reg rd) (fmt_reg rs) (fmt_reg rt)
-  | Syscall -> Printf.sprintf "  syscall"
-  | B l -> Printf.sprintf "  b %s" l
-  | Beqz (r, l) -> Printf.sprintf "  beqz %s, %s" (fmt_reg r) l
-  | Jal l -> Printf.sprintf "  jal %s" l
-  | Jr r -> Printf.sprintf "  jr %s" (fmt_reg r)
+  | Label _ -> ""
+  | _ as i ->
+    Printf.sprintf "  "
+    ^
+    (match i with
+    | Label l -> Printf.sprintf "%s:" l
+    | Li (r, i) -> Printf.sprintf "li %s, %d" (fmt_reg r) i
+    | La (r, a) -> Printf.sprintf "la %s, %s" (fmt_reg r) (fmt_loc a)
+    | Sw (r, a) -> Printf.sprintf "sw %s, %s" (fmt_reg r) (fmt_loc a)
+    | Lw (r, a) -> Printf.sprintf "lw %s, %s" (fmt_reg r) (fmt_loc a)
+    | Sb (r, a) -> Printf.sprintf "sb %s, %s" (fmt_reg r) (fmt_loc a)
+    | Lb (r, a) -> Printf.sprintf "lb %s, %s" (fmt_reg r) (fmt_loc a)
+    | Move (rd, rs) -> Printf.sprintf "move %s, %s" (fmt_reg rd) (fmt_reg rs)
+    | Neg (r, a) -> Printf.sprintf "neg %s, %s" (fmt_reg r) (fmt_reg a)
+    | Addi (rd, rs, i) -> Printf.sprintf "addi %s, %s, %d" (fmt_reg rd) (fmt_reg rs) i
+    | Add (rd, rs, rt) ->
+      Printf.sprintf "add %s, %s, %s" (fmt_reg rd) (fmt_reg rs) (fmt_reg rt)
+    | Mul (rd, rs, rt) ->
+      Printf.sprintf "mul %s, %s, %s" (fmt_reg rd) (fmt_reg rs) (fmt_reg rt)
+    | Syscall -> Printf.sprintf "syscall"
+    | B l -> Printf.sprintf "b %s" l
+    | Beqz (r, l) -> Printf.sprintf "beqz %s, %s" (fmt_reg r) l
+    | Jal l -> Printf.sprintf "jal %s" l
+    | Jr r -> Printf.sprintf "jr %s" (fmt_reg r))
 ;;
 
 let fmt_dir = function