diff --git a/dist/index.js b/dist/index.js
index 43d961f..90a0c5e 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -929,7 +929,7 @@ class Definitions extends Array {
       );
     }
 
-    const duplicateDefaultOption = hasDuplicates(this.map(def => def.defaultOption));
+    const duplicateDefaultOption = this.filter(def => def.defaultOption === true).length > 1;
     if (duplicateDefaultOption) {
       halt(
         'INVALID_DEFINITIONS',
diff --git a/dist/index.mjs b/dist/index.mjs
index f55dfee..00683e4 100644
--- a/dist/index.mjs
+++ b/dist/index.mjs
@@ -925,7 +925,7 @@ class Definitions extends Array {
       );
     }
 
-    const duplicateDefaultOption = hasDuplicates(this.map(def => def.defaultOption));
+    const duplicateDefaultOption = this.filter(def => def.defaultOption === true).length > 1;
     if (duplicateDefaultOption) {
       halt(
         'INVALID_DEFINITIONS',
diff --git a/dist/tests.js b/dist/tests.js
index 7e4cb46..996cc72 100644
--- a/dist/tests.js
+++ b/dist/tests.js
@@ -931,7 +931,7 @@ class Definitions extends Array {
       );
     }
 
-    const duplicateDefaultOption = hasDuplicates(this.map(def => def.defaultOption));
+    const duplicateDefaultOption = this.filter(def => def.defaultOption === true).length > 1;
     if (duplicateDefaultOption) {
       halt(
         'INVALID_DEFINITIONS',
@@ -2350,6 +2350,20 @@ runner$c.test('defaultOption: multiple-defaultOption values spread out', functio
   });
 });
 
+runner$c.test('defaultOption: can be false', function () {
+  const optionDefinitions = [
+    { name: 'one', defaultOption: false },
+    { name: 'two', defaultOption: false },
+    { name: 'files', defaultOption: true, multiple: true }
+  ];
+  const argv = ['--one', '1', 'file1', 'file2', '--two', '2'];
+  a.deepStrictEqual(commandLineArgs(optionDefinitions, { argv }), {
+    one: '1',
+    two: '2',
+    files: ['file1', 'file2']
+  });
+});
+
 runner$c.test('defaultOption: multiple-defaultOption values spread out 2', function () {
   const optionDefinitions = [
     { name: 'one', type: Boolean },
@@ -2761,6 +2775,20 @@ runner$h.test('err-invalid-definition: multiple defaultOption', function () {
   );
 });
 
+runner$h.test('err-invalid-definition: multiple defaultOptions 2', function () {
+  const optionDefinitions = [
+    { name: 'one', defaultOption: undefined },
+    { name: 'two', defaultOption: false },
+    { name: 'files', defaultOption: true, multiple: true },
+    { name: 'files2', defaultOption: true }
+  ];
+  const argv = ['--one', '1', 'file1', 'file2', '--two', '2'];
+  a.throws(
+    () => commandLineArgs(optionDefinitions, { argv }),
+    err => err.name === 'INVALID_DEFINITIONS'
+  );
+});
+
 runner$h.test('err-invalid-defaultOption: defaultOption on a Boolean type', function () {
   const optionDefinitions = [
     { name: 'one', type: Boolean, defaultOption: true }
diff --git a/test/exceptions-invalid-definition.mjs b/test/exceptions-invalid-definition.mjs
index e228a90..a47e32b 100644
--- a/test/exceptions-invalid-definition.mjs
+++ b/test/exceptions-invalid-definition.mjs
@@ -165,6 +165,20 @@ runner.test('err-invalid-definition: multiple defaultOption', function () {
   )
 })
 
+runner.test('err-invalid-definition: multiple defaultOptions 2', function () {
+  const optionDefinitions = [
+    { name: 'one', defaultOption: undefined },
+    { name: 'two', defaultOption: false },
+    { name: 'files', defaultOption: true, multiple: true },
+    { name: 'files2', defaultOption: true }
+  ]
+  const argv = ['--one', '1', 'file1', 'file2', '--two', '2']
+  a.throws(
+    () => commandLineArgs(optionDefinitions, { argv }),
+    err => err.name === 'INVALID_DEFINITIONS'
+  )
+})
+
 runner.test('err-invalid-defaultOption: defaultOption on a Boolean type', function () {
   const optionDefinitions = [
     { name: 'one', type: Boolean, defaultOption: true }