diff --git a/tests/as-int-n.mjs b/tests/as-int-n.mjs
index 641230b..21ebae2 100644
--- a/tests/as-int-n.mjs
+++ b/tests/as-int-n.mjs
@@ -285,9 +285,7 @@ const uintn_data = [
 
 function parse(string) {
   if (string.charCodeAt(0) === 0x2D) { // '-'
-    const result = JSBI.BigInt(string.slice(1));
-    result.sign = true;
-    return result;
+    return JSBI.unaryMinus(JSBI.BigInt(string.slice(1)));
   }
   return JSBI.BigInt(string);
 }
diff --git a/tests/tests.mjs b/tests/tests.mjs
index efca1ab..62d664c 100644
--- a/tests/tests.mjs
+++ b/tests/tests.mjs
@@ -133,9 +133,7 @@ const TESTS = [
 
 function parse(string) {
   if (string.charCodeAt(0) === 0x2D) { // '-'
-    const result = JSBI.BigInt(string.slice(1));
-    result.sign = true;
-    return result;
+    return JSBI.unaryMinus(JSBI.BigInt(string.slice(1)));
   }
   return JSBI.BigInt(string);
 }