diff --git a/custom-standards/Flyeralarm/Sniffs/Docblock/ReturnTypeSniff.php b/custom-standards/Flyeralarm/Sniffs/Docblock/ReturnTypeSniff.php
index 6271637..f7fdb22 100644
--- a/custom-standards/Flyeralarm/Sniffs/Docblock/ReturnTypeSniff.php
+++ b/custom-standards/Flyeralarm/Sniffs/Docblock/ReturnTypeSniff.php
@@ -58,22 +58,13 @@ public function process(File $phpcsFile, $stackPtr)
         $tokens = $phpcsFile->getTokens();
         $returnTypePtr = $this->getDocReturnTypePtr($phpcsFile, $stackPtr);
         $returnTypeString = $tokens[$returnTypePtr]['content'];
-        $returnTypes = explode('|', $returnTypeString);
-
-        foreach ($returnTypes as $returnType) {
-            $returnType = trim($returnType);
-            if (in_array($returnType, $this->returnTypeScalarWhitelist, true)) {
-                continue;
-            }
-            if (in_array($returnType, $this->returnTypeClassWhitelist, true)) {
-                continue;
-            }
-            if ($this->isStartingWithUppercaseLetter($returnType)) {
-                continue;
-            }
 
+        try {
+            $this->checkReturnTypeShape($returnTypeString);
+        }
+        catch (\InvalidArgumentException $exception) {
             $phpcsFile->addError(
-                sprintf('Return type "%s" is discouraged', $returnType),
+                $exception->getMessage(),
                 $returnTypePtr,
                 'ProhibitedReturnType'
             );
@@ -145,4 +136,55 @@ private function isStartingWithUppercaseLetter($singleCharacter)
 
         return false;
     }
+
+    /**
+     * @param string $subject The return type string to check.
+     * @return void
+     */
+    private function checkReturnTypeShape(string $subject)
+    {
+        $matched = preg_match_all('#(?<separator>\s*\|\s*)?(?<atom>[^<>\|]+)(?<generic><(?<nested>.*)>)?#', $subject, $matches);
+
+        if (!$matched || implode('', $matches[0]) !== $subject) {
+            throw new \InvalidArgumentException('Invalid structure in return type "' . $subject . '"');
+        }
+
+        if (strpos($matches['separator'][0], '|') !== false) {
+            throw new \InvalidArgumentException('Missing return type in first alternative of type "' . $subject . '"');
+        }
+
+        foreach ($matches['nested'] as $index => $match) {
+            if ($matches['generic'][$index] === '') {
+                if (trim($matches['atom'][$index]) !== 'array') {
+                    throw new \InvalidArgumentException('Unexpected generic specification in type "' . $matches[0][$index] . '"');
+                }
+
+                $match = trim($match);
+                if (strpos($match, 'int,') === 0) {
+                    // Allow numeric indexing in generics, e.g. `array<int, string>`
+                    $match = substr($match, 4);
+                }
+
+                if ($match === '') {
+                    throw new \InvalidArgumentException('Generic specification may not be empty in type "' . $matches[0][$index] . '"');
+                }
+
+                $this->checkReturnTypeShape($match);
+            }
+
+            // Check if atom is in whitelist.
+            $returnType = trim($matches['atom'][$index]);
+            if (in_array($returnType, $this->returnTypeScalarWhitelist, true)) {
+                continue;
+            }
+            if (in_array($returnType, $this->returnTypeClassWhitelist, true)) {
+                continue;
+            }
+            if ($this->isStartingWithUppercaseLetter($returnType)) {
+                continue;
+            }
+
+            throw new \InvalidArgumentException('Return type "' . $returnType . '" is discouraged');
+        }
+    }
 }
diff --git a/tests/rules/doc/allowed/ReturnTypeArrayGenerics.php b/tests/rules/doc/allowed/ReturnTypeArrayGenerics.php
new file mode 100644
index 0000000..93082b6
--- /dev/null
+++ b/tests/rules/doc/allowed/ReturnTypeArrayGenerics.php
@@ -0,0 +1,57 @@
+<?php
+
+// @expectedPass
+
+namespace flyeralarm\Test;
+
+class FooTest
+{
+    /**
+     * @return array
+     */
+    public function testArray()
+    {
+    }
+
+    /**
+     * @return array<string>
+     */
+    public function testWithGeneric()
+    {
+    }
+
+    /**
+     * @return array<int, string>
+     */
+    public function testWithNumericIndex()
+    {
+    }
+
+    /**
+     * @return array<string | int>
+     */
+    public function testWithAlternativeInside()
+    {
+    }
+
+    /**
+     * @return int | array<array<string>>
+     */
+    public function testWithAlternativeOutside()
+    {
+    }
+
+    /**
+     * @return array<array<string>> | null
+     */
+    public function testWithAlternativeAtTheEnd()
+    {
+    }
+
+    /**
+     * @return int | array<string | array<string>>
+     */
+    public function testWithMultipleAlternatives()
+    {
+    }
+}
diff --git a/tests/rules/doc/not-allowed/EmptyAlternativeInReturnTypeInDocComment.php b/tests/rules/doc/not-allowed/EmptyAlternativeInReturnTypeInDocComment.php
new file mode 100644
index 0000000..f1cfe5d
--- /dev/null
+++ b/tests/rules/doc/not-allowed/EmptyAlternativeInReturnTypeInDocComment.php
@@ -0,0 +1,14 @@
+<?php
+
+// @expectedError Missing return type in first alternative of type "| string"
+
+class EmptyAlternativeInReturnTypeInDocComment
+{
+    /**
+     * @return | string
+     */
+    public function foo()
+    {
+        return true;
+    }
+}
diff --git a/tests/rules/doc/not-allowed/EmptyGenericReturnTypeInDocComment.php b/tests/rules/doc/not-allowed/EmptyGenericReturnTypeInDocComment.php
new file mode 100644
index 0000000..88c4400
--- /dev/null
+++ b/tests/rules/doc/not-allowed/EmptyGenericReturnTypeInDocComment.php
@@ -0,0 +1,14 @@
+<?php
+
+// @expectedError Generic specification may not be empty in type "array<>"
+
+class EmptyGenericReturnTypeInDocComment
+{
+    /**
+     * @return array<>
+     */
+    public function foo()
+    {
+        return true;
+    }
+}
diff --git a/tests/rules/doc/not-allowed/InvalidStructureInReturnTypeInDocComment.php b/tests/rules/doc/not-allowed/InvalidStructureInReturnTypeInDocComment.php
new file mode 100644
index 0000000..f446ab9
--- /dev/null
+++ b/tests/rules/doc/not-allowed/InvalidStructureInReturnTypeInDocComment.php
@@ -0,0 +1,14 @@
+<?php
+
+// @expectedError Invalid structure in return type "array<int"
+
+class InvalidStructureInReturnTypeInDocComment
+{
+    /**
+     * @return array<int
+     */
+    public function foo()
+    {
+        return true;
+    }
+}
diff --git a/tests/rules/doc/not-allowed/MissingAlternativeSeparatorInReturnTypeInDocComment.php b/tests/rules/doc/not-allowed/MissingAlternativeSeparatorInReturnTypeInDocComment.php
new file mode 100644
index 0000000..987b398
--- /dev/null
+++ b/tests/rules/doc/not-allowed/MissingAlternativeSeparatorInReturnTypeInDocComment.php
@@ -0,0 +1,14 @@
+<?php
+
+// @expectedError Return type "array int" is discouraged
+
+class MissingAlternativeSeparatorInReturnTypeInDocComment
+{
+    /**
+     * @return array int
+     */
+    public function foo()
+    {
+        return true;
+    }
+}
diff --git a/tests/rules/doc/not-allowed/UnknownGenericReturnTypeInDocComment.php b/tests/rules/doc/not-allowed/UnknownGenericReturnTypeInDocComment.php
new file mode 100644
index 0000000..e35d38e
--- /dev/null
+++ b/tests/rules/doc/not-allowed/UnknownGenericReturnTypeInDocComment.php
@@ -0,0 +1,14 @@
+<?php
+
+// @expectedError Unexpected generic specification in type "int<array>"
+
+class UnknownGenericReturnTypeInDocComment
+{
+    /**
+     * @return int<array>
+     */
+    public function foo()
+    {
+        return true;
+    }
+}
diff --git a/tests/rules/doc/not-allowed/UnknownGenericSubReturnTypeInDocComment.php b/tests/rules/doc/not-allowed/UnknownGenericSubReturnTypeInDocComment.php
new file mode 100644
index 0000000..769521f
--- /dev/null
+++ b/tests/rules/doc/not-allowed/UnknownGenericSubReturnTypeInDocComment.php
@@ -0,0 +1,14 @@
+<?php
+
+// @expectedError Return type "foo" is discouraged
+
+class UnknownGenericSubReturnTypeInDocComment
+{
+    /**
+     * @return array<foo>
+     */
+    public function foo()
+    {
+        return true;
+    }
+}