diff --git a/src/Csv.php b/src/Csv.php
index fb4dad4..a85f819 100644
--- a/src/Csv.php
+++ b/src/Csv.php
@@ -15,7 +15,7 @@ public function __construct(string $filePath)
         );
     }
 
-    public static function make(array $data)
+    public static function write(array $data)
     {
         return new CsvWriter($data);
     }
diff --git a/src/CsvWriter.php b/src/CsvWriter.php
index 564b941..f4702b6 100644
--- a/src/CsvWriter.php
+++ b/src/CsvWriter.php
@@ -13,21 +13,26 @@ public function __construct(array $data)
         $this->data = $data;
     }
 
-    public function toFile(string $filePath)
+    public function toFile(string $filePath, $append = false)
     {
-        $handle = fopen($filePath, 'w');
+        $fileMode = $append ? 'a' : 'w';
+        $handle = fopen($filePath, $fileMode);
+        if ($handle === false) {
+            throw new \Exception("Could not open file: $filePath");
+        }
+
+        if ($append === true) {
+            $headers = fgetcsv(fopen($filePath, 'r'));
+            $this->headers = $headers;
+        }
 
-        if ($this->headers !== []) {
+        if ($this->headers !== [] && $append === false) {
             fputcsv($handle, $this->headers);
         }
 
         foreach ($this->data as $row) {
             if ($this->headers !== []) {
-                // if the keys of the row are strings, then we need to merge the headers with the row
-                // so that the keys are in the same order as the headers
-                if (array_keys($row) !== range(0, count($row) - 1)) {
-                    $row = array_merge(array_flip($this->headers), $row);
-                }
+                $row = $this->normalizeRowWithHeaders($row);
             }
 
             fputcsv($handle, $row);
@@ -43,4 +48,15 @@ public function withHeaders(array $headers)
 
         return $this;
     }
+
+    protected function normalizeRowWithHeaders($row)
+    {
+        // if the keys of the row are strings, then we need to merge the headers with the row
+        // so that the keys are in the same order as the headers
+        if (array_keys($row) !== range(0, count($row) - 1)) {
+            return array_merge(array_flip($this->headers), $row);
+        }
+
+        return $row;
+    }
 }
diff --git a/tests/Fixtures/data_write.csv b/tests/Fixtures/data_write.csv
index 997d2bc..3e38485 100644
--- a/tests/Fixtures/data_write.csv
+++ b/tests/Fixtures/data_write.csv
@@ -1,2 +1,3 @@
 Col1,Col2,Col3
 Foo,Bar,Baz
+Foo2,Bar2,Baz2
diff --git a/tests/Unit/CsvWriteTest.php b/tests/Unit/CsvWriteTest.php
index 55c7f70..f3b71a4 100644
--- a/tests/Unit/CsvWriteTest.php
+++ b/tests/Unit/CsvWriteTest.php
@@ -9,7 +9,7 @@
         'Baz',
     ]];
 
-    $file = Csv::make($data)
+    $file = Csv::write($data)
         ->toFile(__DIR__.'/../Fixtures/data_write.csv');
 
     expect(file_get_contents(__DIR__.'/../Fixtures/data_write.csv'))
@@ -25,7 +25,7 @@
     ],
     ];
 
-    $file = Csv::make($data)
+    $file = Csv::write($data)
         ->withHeaders(['Col1', 'Col2', 'Col3'])
         ->toFile(__DIR__.'/../Fixtures/data_write.csv');
 
@@ -47,13 +47,13 @@
         ],
     ];
 
-    $file = Csv::make($data)
+    $file = Csv::write($data)
         ->withHeaders(['Col1', 'Col2', 'Col3'])
         ->toFile(__DIR__.'/../Fixtures/data_write.csv');
 
     $foo = file_get_contents(__DIR__.'/../Fixtures/data_write.csv');
 
-    expect(file_get_contents(__DIR__.'/../Fixtures/data_write.csv'))
+    expect($foo)
         ->toBe(
             'Col1,Col2,Col3'.PHP_EOL.
             'Foo,Bar,Baz'.PHP_EOL
@@ -68,25 +68,64 @@
     ],
     ];
 
-    $file = Csv::make($data)
+    $file = Csv::write($data)
         ->withHeaders(['Col1', 'Col2', 'Col3'])
         ->toFile(__DIR__.'/../Fixtures/data_write.csv');
 
+    expect(file_get_contents(__DIR__.'/../Fixtures/data_write.csv'))
+        ->toBe(
+            'Col1,Col2,Col3'.PHP_EOL.
+            'Foo,Bar,Baz'.PHP_EOL
+        );
     $data = [[
         'Foo',
         'Bar',
         'Baz',
-    ],
+    ]];
+    $file = Csv::write($data)
+        ->toFile(__DIR__.'/../Fixtures/data_write.csv', true);
+
+    expect(file_get_contents(__DIR__.'/../Fixtures/data_write.csv'))
+        ->toBe(
+            'Col1,Col2,Col3'.PHP_EOL.
+            'Foo,Bar,Baz'.PHP_EOL.
+            'Foo,Bar,Baz'.PHP_EOL
+        );
+});
+
+test('It appends assoc data to a file in the right order', function () {
+    $data = [
+        [
+            'Col2' => 'Bar',
+            'Col1' => 'Foo',
+            'Col3' => 'Baz',
+        ],
     ];
 
-    $file = Csv::make($data)
+    $file = Csv::write($data)
         ->withHeaders(['Col1', 'Col2', 'Col3'])
-        ->toFile(__DIR__.'/../Fixtures/data_write.csv', 'a');
+        ->toFile(__DIR__.'/../Fixtures/data_write.csv');
 
     expect(file_get_contents(__DIR__.'/../Fixtures/data_write.csv'))
         ->toBe(
             'Col1,Col2,Col3'.PHP_EOL.
-            'Foo,Bar,Baz'.PHP_EOL.
             'Foo,Bar,Baz'.PHP_EOL
         );
+    $data = [
+        [
+            'Col2' => 'Bar2',
+            'Col1' => 'Foo2',
+            'Col3' => 'Baz2',
+        ],
+    ];
+    $file = Csv::write($data)
+        ->withHeaders(['Col1', 'Col2', 'Col3'])
+        ->toFile(__DIR__.'/../Fixtures/data_write.csv', true);
+
+    expect(file_get_contents(__DIR__.'/../Fixtures/data_write.csv'))
+        ->toBe(
+            'Col1,Col2,Col3'.PHP_EOL.
+            'Foo,Bar,Baz'.PHP_EOL.
+            'Foo2,Bar2,Baz2'.PHP_EOL
+        );
 });