diff --git a/lib/chai/core/assertions.js b/lib/chai/core/assertions.js
index c22ba417..c4da00c1 100644
--- a/lib/chai/core/assertions.js
+++ b/lib/chai/core/assertions.js
@@ -3013,8 +3013,10 @@ function closeTo(expected, delta, msg) {
   new Assertion(delta, flagMsg, ssfi, true).is.numeric;
   new Assertion(expected, flagMsg, ssfi, true).is.numeric;
 
+  const abs = (x) => x < 0n ? -x : x;
+
   this.assert(
-      Math.abs(obj - expected) <= delta
+      abs(obj - expected) <= delta
     , 'expected #{this} to be close to ' + expected + ' +/- ' + delta
     , 'expected #{this} not to be close to ' + expected + ' +/- ' + delta
   );
diff --git a/test/assert.js b/test/assert.js
index 5ab8ca8f..747b2719 100644
--- a/test/assert.js
+++ b/test/assert.js
@@ -1877,6 +1877,7 @@ describe('assert', function () {
     assert.approximately(1.5, 1.0, 0.5);
     assert.approximately(10, 20, 20);
     assert.approximately(-10, 20, 30);
+    assert.approximately(1n, 2n, 1n);
 
     err(function(){
       assert.approximately(2, 1.0, 0.5, 'blah');