diff --git a/lib/script/opcode.js b/lib/script/opcode.js
index 246dd980..8c15e246 100644
--- a/lib/script/opcode.js
+++ b/lib/script/opcode.js
@@ -207,6 +207,9 @@ Opcode.prototype.toSmall = function toSmall() {
  */
 
 Opcode.prototype.toNum = function toNum(minimal, limit) {
+  if (this.value === opcodes.OP_1NEGATE)
+    return ScriptNum.fromInt(-1);
+
   const smi = this.toSmall();
 
   if (smi !== -1)