1 files changed, 9 insertions, 0 deletions

diff --git a/parse-events.c b/parse-events.c
index df6ad6e..5f136a7 100644
--- a/parse-events.c
+++ b/parse-events.c
@@ -1597,6 +1597,15 @@ static long long arg_num_eval(struct print_arg *arg)
                                 die("unknown op '%s'", arg->op.op);
                         }
                         break;
+                case '-':
+                        /* check for negative */
+                        if (arg->op.left->type == PRINT_NULL)
+                                left = 0;
+                        else
+                                left = arg_num_eval(arg->op.left);
+                        right = arg_num_eval(arg->op.right);
+                        val = left - right;
+                        break;
                 default:
                         die("unknown op '%s'", arg->op.op);
                 }