diff --git a/baselib.ml b/baselib.ml
index b27515b..0c899b4 100644
--- a/baselib.ml
+++ b/baselib.ml
@@ -18,6 +18,7 @@ let _types_ =
        ; "puti", Func_t (Void_t, [ Int_t ])
        ; "puts", Func_t (Void_t, [ Str_t ])
        ; "geti", Func_t (Int_t, [])
+       ; "abs", Func_t (Int_t, [ Int_t ])
        ])
 ;;
 
@@ -38,5 +39,6 @@ let builtins =
     ; "puti", [ Lw (A0, Mem (SP, 0)); Li (V0, Syscall.print_int); Syscall ]
     ; "puts", [ Lw (A0, Mem (SP, 0)); Li (V0, Syscall.print_str); Syscall ]
     ; "geti", [ Lw (A0, Mem (SP, 0)); Li (V0, Syscall.read_int); Syscall ]
+    ; "abs", [ Lw (T0, Mem (SP, 0)); Abs (V0, T0) ]
     ]
 ;;
diff --git a/mips.ml b/mips.ml
index 7b9f14d..67b47d5 100644
--- a/mips.ml
+++ b/mips.ml
@@ -47,6 +47,7 @@ type instr =
   | Mul of reg * reg * reg
   | Sub of reg * reg * reg
   | Div of reg * reg * reg
+  | Abs of reg * reg
   | Seq of reg * reg * reg
   | Sge of reg * reg * reg
   | Sgt of reg * reg * reg
@@ -131,6 +132,7 @@ let fmt_instr ?(indent = "  ") = function
     Printf.sprintf "%ssub %s, %s, %s" indent (fmt_reg rd) (fmt_reg rs) (fmt_reg rt)
   | Div (rd, rs, rt) ->
     Printf.sprintf "%sdiv %s, %s, %s" indent (fmt_reg rd) (fmt_reg rs) (fmt_reg rt)
+  | Abs (rd, rs) -> Printf.sprintf "%sabs %s, %s" indent (fmt_reg rd) (fmt_reg rs)
   | Seq (rd, rs, rt) ->
     Printf.sprintf "%sseq %s, %s, %s" indent (fmt_reg rd) (fmt_reg rs) (fmt_reg rt)
   | Sge (rd, rs, rt) ->
diff --git a/tests/10_math.test b/tests/10_math.test
index 956c93e..211cd95 100644
--- a/tests/10_math.test
+++ b/tests/10_math.test
@@ -1,4 +1,4 @@
 void main () {
-    int res = 13 * 100 + 20 - 8;
-    res = res * 2 / 2;
+    int res = 13 * -100 - 20 + 8;
+    res = abs(res * 2) / 2;
 }