diff --git a/.scrutinizer.yml b/.scrutinizer.yml
index 01162324..7831329e 100644
--- a/.scrutinizer.yml
+++ b/.scrutinizer.yml
@@ -1,9 +1,20 @@
+build:
+    nodes:
+        analysis:
+            project_setup:
+                override: true
+            tests:
+                override:
+                    - php-scrutinizer-run --enable-security-analysis
 filter:
-    paths: [src/*]
-    excluded_paths: [tests/*]
+    paths:
+        - src/
+    excluded_paths:
+        - tests/
 checks:
     php:
         code_rating: true
+        duplication: true
 tools:
     external_code_coverage:
         timeout: 600
@@ -11,7 +22,11 @@ tools:
     php_code_coverage: false
     php_loc:
         enabled: true
-        excluded_dirs: [tests, vendor]
-    php_cpd:
+        excluded_dirs:
+            - tests/
+            - vendor/
+    php_cpd: false
+    php_sim:
         enabled: true
-        excluded_dirs: [tests, vendor]
+        filter:
+            paths: ['src/']
\ No newline at end of file
diff --git a/.travis.yml b/.travis.yml
index 408252e7..a0065fad 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -29,8 +29,8 @@ install:
 
 script:
   - composer phpunit
+  - if [ "$VALIDATE_CODING_STYLE" == "true" ]; then composer phpcs; fi
+  - if [ "$RUN_PHPSTAN" == "true" ]; then composer phpstan; fi
 
 after_script:
  - if [ "$COLLECT_COVERAGE" == "true" ]; then wget https://scrutinizer-ci.com/ocular.phar && php ocular.phar code-coverage:upload --format=php-clover build/clover.xml; fi
- - if [ "$VALIDATE_CODING_STYLE" == "true" ]; then composer phpcs; fi
- - if [ "$RUN_PHPSTAN" == "true" ]; then composer phpstan; fi
diff --git a/src/CharsetConverter.php b/src/CharsetConverter.php
index 671839fd..99600608 100644
--- a/src/CharsetConverter.php
+++ b/src/CharsetConverter.php
@@ -208,17 +208,17 @@ public function __invoke(array $record): array
     /**
      * Walker method to convert the offset and the value of a CSV record field
      *
-     * @param string|null $value
-     * @param string|int  $offset
+     * @param mixed $value
+     * @param mixed $offset
      */
     protected function encodeField(&$value, &$offset)
     {
-        if (null !== $value) {
-            $value = mb_convert_encoding($value, $this->output_encoding, $this->input_encoding);
+        if (null !== $value && !is_numeric($value)) {
+            $value = mb_convert_encoding((string) $value, $this->output_encoding, $this->input_encoding);
         }
 
-        if (!is_int($offset)) {
-            $offset = mb_convert_encoding($offset, $this->output_encoding, $this->input_encoding);
+        if (!is_numeric($offset)) {
+            $offset = mb_convert_encoding((string) $offset, $this->output_encoding, $this->input_encoding);
         }
     }
 
diff --git a/src/Writer.php b/src/Writer.php
index 645a0876..557f0342 100644
--- a/src/Writer.php
+++ b/src/Writer.php
@@ -129,7 +129,7 @@ public function insertOne(array $record): int
         $record = array_reduce($this->formatters, [$this, 'formatRecord'], $record);
         $this->validateRecord($record);
         $bytes = $this->document->fputcsv($record, $this->delimiter, $this->enclosure, $this->escape);
-        if (false !== $bytes && null !== $bytes) {
+        if ('' !== (string) $bytes) {
             return $bytes + $this->consolidate();
         }
 
diff --git a/tests/CharsetConverterTest.php b/tests/CharsetConverterTest.php
index 3bee2f7d..6f4f8e48 100644
--- a/tests/CharsetConverterTest.php
+++ b/tests/CharsetConverterTest.php
@@ -150,4 +150,43 @@ public function testOnCreateFailedWithWrongParams()
         $converter->filtername = CharsetConverter::FILTERNAME.'.foo/bar';
         $this->assertFalse($converter->onCreate());
     }
+
+    /**
+     * @covers ::convert
+     * @covers ::encodeField
+     *
+     * @dataProvider converterProvider
+     * @param array $record
+     * @param array $expected
+     */
+    public function testConvertOnlyStringField(array $record, array $expected)
+    {
+        $converter = (new CharsetConverter())
+            ->inputEncoding('iso-8859-15')
+            ->outputEncoding('utf-8');
+        $res = $converter->convert([$record]);
+        $this->assertSame($expected, $res[0]);
+    }
+
+    public function converterProvider()
+    {
+        return [
+            'only numeric values' => [
+                'record' => [1, 2, 3],
+                'expected' => [1, 2, 3],
+            ],
+            'only string values' => [
+                'record' => ['1', '2', '3'],
+                'expected' => ['1', '2', '3'],
+            ],
+            'mixed values' => [
+                'record' => [1, '2', 3],
+                'expected' => [1, '2', 3],
+            ],
+            'mixed offset' => [
+                'record' => [1 => 1, '2' => '2', 3 => 3],
+                'expected' => [1 => 1, '2' => '2', 3 => 3],
+            ],
+        ];
+    }
 }