diff --git a/src/parser/calculate_size.ts b/src/parser/calculate_size.ts
index 923beeb0..da62ae6c 100644
--- a/src/parser/calculate_size.ts
+++ b/src/parser/calculate_size.ts
@@ -205,6 +205,9 @@ function calculateElement(
           1
         );
       }
+      return 0;
+    case 'bigint':
+      return (name != null ? ByteUtils.utf8ByteLength(name) + 1 : 0) + (8 + 1);
   }
 
   return 0;
diff --git a/test/node/parser/calculate_size.test.ts b/test/node/parser/calculate_size.test.ts
index 3ebccd16..e421c28f 100644
--- a/test/node/parser/calculate_size.test.ts
+++ b/test/node/parser/calculate_size.test.ts
@@ -24,4 +24,10 @@ describe('calculateSize()', () => {
       })
     ).to.throw(BSONVersionError, /Unsupported BSON version/i);
   });
+
+  it('returns the correct size for a bigint value', function () {
+    const doc = { a: BigInt(1) };
+    expect(BSON.calculateObjectSize(doc)).to.equal(16);
+    expect(BSON.calculateObjectSize(doc)).to.equal(BSON.serialize(doc).byteLength);
+  });
 });