diff --git a/.gitattributes b/.gitattributes
index 4e57adf..3dd7607 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -2,5 +2,6 @@
 .github export-ignore
 .gitignore export-ignore
 phpstan.neon.dist export-ignore
+phpstan-baseline.neon export-ignore
 phpunit.xml.dist export-ignore
 /tests export-ignore
diff --git a/README.md b/README.md
index ab4346d..e658f72 100644
--- a/README.md
+++ b/README.md
@@ -35,6 +35,7 @@ You can also pass additional flags to `JsonParser::lint/parse` that tweak the fu
 - `JsonParser::ALLOW_DUPLICATE_KEYS` collects duplicate keys. e.g. if you have two `foo` keys they will end up as `foo` and `foo.2`.
 - `JsonParser::PARSE_TO_ASSOC` parses to associative arrays instead of stdClass objects.
 - `JsonParser::ALLOW_COMMENTS` parses while allowing (and ignoring) inline `//` and multiline `/* */` comments in the JSON document.
+- `JsonParser::ALLOW_DUPLICATE_KEYS_TO_ARRAY` collects duplicate keys. e.g. if you have two `foo` keys the `foo` key will become an object (or array in assoc mode) with all `foo` values accessible as an array in `$result->foo->__duplicates__` (or `$result['foo']['__duplicates__']` in assoc mode).
 
 Example:
 
diff --git a/composer.json b/composer.json
index 3f8afc5..dbc48e3 100644
--- a/composer.json
+++ b/composer.json
@@ -16,7 +16,7 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^4.8.35 || ^5.7 || ^6.0 || ^8.5.13",
-        "phpstan/phpstan": "^1.5"
+        "phpstan/phpstan": "^1.11"
     },
     "autoload": {
         "psr-4": { "Seld\\JsonLint\\": "src/Seld/JsonLint/" }
diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
new file mode 100644
index 0000000..bce1ff3
--- /dev/null
+++ b/phpstan-baseline.neon
@@ -0,0 +1,16 @@
+parameters:
+	ignoreErrors:
+		-
+			message: "#^Cannot access offset 1 on array\\|bool\\|float\\|int\\|stdClass\\|string\\|null\\.$#"
+			count: 1
+			path: src/Seld/JsonLint/JsonParser.php
+
+		-
+			message: "#^Property Seld\\\\JsonLint\\\\JsonParser\\:\\:\\$vstack \\(list\\<array\\|bool\\|float\\|int\\|stdClass\\|string\\|null\\>\\) does not accept non\\-empty\\-array\\<int\\<\\-3, max\\>, array\\|bool\\|float\\|int\\|stdClass\\|string\\|null\\>\\.$#"
+			count: 4
+			path: src/Seld/JsonLint/JsonParser.php
+
+		-
+			message: "#^Property Seld\\\\JsonLint\\\\JsonParser\\:\\:\\$vstack \\(list\\<array\\|bool\\|float\\|int\\|stdClass\\|string\\|null\\>\\) does not accept non\\-empty\\-array\\<int\\<\\-3, max\\>, mixed\\>\\.$#"
+			count: 1
+			path: src/Seld/JsonLint/JsonParser.php
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index aa3323d..bd3a0ec 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -1,6 +1,12 @@
+includes:
+    - phpstan-baseline.neon
+    - vendor/phpstan/phpstan/conf/bleedingEdge.neon
+
 parameters:
     level: 8
 
+    treatPhpDocTypesAsCertain: false
+
     paths:
         - src/
         - tests/
diff --git a/src/Seld/JsonLint/JsonParser.php b/src/Seld/JsonLint/JsonParser.php
index 420c0fd..cec4a87 100644
--- a/src/Seld/JsonLint/JsonParser.php
+++ b/src/Seld/JsonLint/JsonParser.php
@@ -31,6 +31,7 @@ class JsonParser
     const ALLOW_DUPLICATE_KEYS = 2;
     const PARSE_TO_ASSOC = 4;
     const ALLOW_COMMENTS = 8;
+    const ALLOW_DUPLICATE_KEYS_TO_ARRAY = 16;
 
     /** @var Lexer */
     private $lexer;
@@ -201,6 +202,10 @@ public function lint($input, $flags = 0)
      */
     public function parse($input, $flags = 0)
     {
+        if (($flags & self::ALLOW_DUPLICATE_KEYS_TO_ARRAY) && ($flags & self::ALLOW_DUPLICATE_KEYS)) {
+            throw new \InvalidArgumentException('Only one of ALLOW_DUPLICATE_KEYS and ALLOW_DUPLICATE_KEYS_TO_ARRAY can be used, you passed in both.');
+        }
+
         $this->failOnBOM($input);
 
         $this->flags = $flags;
@@ -334,7 +339,7 @@ public function parse($input, $flags = 0)
             }
 
             // this shouldn't happen, unless resolve defaults are off
-            if (\is_array($action[0]) && \count($action) > 1) { // @phpstan-ignore-line
+            if (\is_array($action[0]) && \count($action) > 1) {
                 throw new ParsingException('Parse Error: multiple actions possible at state: ' . $state . ', token: ' . $symbol);
             }
 
@@ -484,14 +489,21 @@ private function performAction($currentToken, $yytext, $yyleng, $yylineno, $yyst
                     $errStr .= $this->lexer->showPosition() . "\n";
                     $errStr .= "Duplicate key: ".$this->vstack[$len][0];
                     throw new DuplicateKeyException($errStr, $this->vstack[$len][0], array('line' => $yylineno+1));
-                } elseif (($this->flags & self::ALLOW_DUPLICATE_KEYS) && isset($this->vstack[$len-2][$key])) {
+                }
+                if (($this->flags & self::ALLOW_DUPLICATE_KEYS) && isset($this->vstack[$len-2][$key])) {
                     $duplicateCount = 1;
                     do {
                         $duplicateKey = $key . '.' . $duplicateCount++;
                     } while (isset($this->vstack[$len-2][$duplicateKey]));
-                    $key = $duplicateKey;
+                    $this->vstack[$len-2][$duplicateKey] = $this->vstack[$len][1];
+                } elseif (($this->flags & self::ALLOW_DUPLICATE_KEYS_TO_ARRAY) && isset($this->vstack[$len-2][$key])) {
+                    if (!isset($this->vstack[$len-2][$key]['__duplicates__']) || !is_array($this->vstack[$len-2][$key]['__duplicates__'])) {
+                        $this->vstack[$len-2][$key] = array('__duplicates__' => array($this->vstack[$len-2][$key]));
+                    }
+                    $this->vstack[$len-2][$key]['__duplicates__'][] = $this->vstack[$len][1];
+                } else {
+                    $this->vstack[$len-2][$key] = $this->vstack[$len][1];
                 }
-                $this->vstack[$len-2][$key] = $this->vstack[$len][1];
             } else {
                 assert($this->vstack[$len-2] instanceof stdClass);
                 $token = $this->vstack[$len-2];
@@ -500,19 +512,26 @@ private function performAction($currentToken, $yytext, $yyleng, $yylineno, $yyst
                 } else {
                     $key = $this->vstack[$len][0];
                 }
-                if (($this->flags & self::DETECT_KEY_CONFLICTS) && isset($this->vstack[$len-2]->{$key})) {
+                if (($this->flags & self::DETECT_KEY_CONFLICTS) && isset($this->vstack[$len-2]->$key)) {
                     $errStr = 'Parse error on line ' . ($yylineno+1) . ":\n";
                     $errStr .= $this->lexer->showPosition() . "\n";
                     $errStr .= "Duplicate key: ".$this->vstack[$len][0];
                     throw new DuplicateKeyException($errStr, $this->vstack[$len][0], array('line' => $yylineno+1));
-                } elseif (($this->flags & self::ALLOW_DUPLICATE_KEYS) && isset($this->vstack[$len-2]->{$key})) {
+                }
+                if (($this->flags & self::ALLOW_DUPLICATE_KEYS) && isset($this->vstack[$len-2]->$key)) {
                     $duplicateCount = 1;
                     do {
                         $duplicateKey = $key . '.' . $duplicateCount++;
                     } while (isset($this->vstack[$len-2]->$duplicateKey));
-                    $key = $duplicateKey;
+                    $this->vstack[$len-2]->$duplicateKey = $this->vstack[$len][1];
+                } elseif (($this->flags & self::ALLOW_DUPLICATE_KEYS_TO_ARRAY) && isset($this->vstack[$len-2]->$key)) {
+                    if (!isset($this->vstack[$len-2]->$key->__duplicates__)) {
+                        $this->vstack[$len-2]->$key = (object) array('__duplicates__' => array($this->vstack[$len-2]->$key));
+                    }
+                    $this->vstack[$len-2]->$key->__duplicates__[] = $this->vstack[$len][1];
+                } else {
+                    $this->vstack[$len-2]->$key = $this->vstack[$len][1];
                 }
-                $this->vstack[$len-2]->$key = $this->vstack[$len][1];
             }
             break;
         case 18:
diff --git a/tests/JsonParserTest.php b/tests/JsonParserTest.php
index 3eb73c2..9b903bf 100644
--- a/tests/JsonParserTest.php
+++ b/tests/JsonParserTest.php
@@ -231,7 +231,9 @@ public function testDuplicateKeys()
     {
         $parser = new JsonParser();
 
-        $result = $parser->parse('{"a":"b", "a":"c", "a":"d"}', JsonParser::ALLOW_DUPLICATE_KEYS);
+        $str = '{"a":"b", "a":"c", "a":"d"}';
+
+        $result = $parser->parse($str, JsonParser::ALLOW_DUPLICATE_KEYS);
         $this->assertThat($result,
             $this->logicalAnd(
                 $this->objectHasAttribute('a'),
@@ -239,6 +241,24 @@ public function testDuplicateKeys()
                 $this->objectHasAttribute('a.2')
             )
         );
+
+        $result = $parser->parse($str, JsonParser::ALLOW_DUPLICATE_KEYS | JsonParser::PARSE_TO_ASSOC);
+        self::assertSame(array('a' => 'b', 'a.1' => 'c', 'a.2' => 'd'), $result);
+    }
+
+    public function testDuplicateKeysToArray()
+    {
+        $parser = new JsonParser();
+
+        $str = '{"a":"b", "a":"c", "a":"d"}';
+
+        $result = $parser->parse($str, JsonParser::ALLOW_DUPLICATE_KEYS_TO_ARRAY);
+        $this->assertThat($result, $this->objectHasAttribute('a'));
+        $this->assertThat($result->a, $this->objectHasAttribute('__duplicates__'));
+        self::assertSame(array('b', 'c', 'd'), $result->a->__duplicates__);
+
+        $result = $parser->parse($str, JsonParser::ALLOW_DUPLICATE_KEYS_TO_ARRAY | JsonParser::PARSE_TO_ASSOC);
+        self::assertSame(array('a' => array('__duplicates__' => array('b', 'c', 'd'))), $result);
     }
 
     public function testDuplicateKeysWithEmpty()