diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 010e5a6..742a10a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,5 +30,8 @@ jobs:
       - name: Run tests
         run: ./vendor/bin/phpunit
 
+      - name: Run static analysis
+        run: ./vendor/bin/phpstan analyse
+
       - name: Verify documentation
         run: ./vendor/bin/mddoc --dry-run
diff --git a/README.md b/README.md
index dfe1640..13c67f5 100644
--- a/README.md
+++ b/README.md
@@ -29,29 +29,29 @@ function array_flatten(array $array, $allow_duplicates = false)
 
 ##### Parameters
 
-- ***array*** `$array` - The Array to be Flattened
+- ***array<array-key,mixed>*** `$array` - The Array to be Flattened
 - ***bool*** `$allow_duplicates` - Should the array allow duplicates
 
 ##### Return Value
 
-- ***array*** - The resulting array or NULL on failure
+- ***array<array-key,mixed>*** - The resulting array or NULL on failure
 
 Given an array, find all the values recursively.
 
 ### Function: \array_blend
 
 ```php
-function array_blend(array $arrays, array $keys = null)
+function array_blend(array $arrays, ?array $keys = null)
 ```
 
 ##### Parameters
 
-- ***array*** `$arrays` - An array of arrays.
-- ***array*** | ***null*** `$keys` - The merged array.
+- ***array<array-key,mixed>*** `$arrays` - An array of arrays.
+- ***array<array-key,array-key>*** | ***null*** `$keys` - The merged array.
 
 ##### Return Value
 
-- ***array*** - The resulting blended array
+- ***array<array-key,mixed>*** - The resulting blended array
 
 Given an array of arrays, merges the array's children together.
 
@@ -63,12 +63,12 @@ function array_key_array(array $arrays, $key)
 
 ##### Parameters
 
-- ***array*** `$arrays` - An array of similarly keyed arrays
-- ***int*** | ***string*** `$key` - The desired key
+- ***array<array-key,array<array-key,mixed>>*** `$arrays` - An array of similarly keyed arrays
+- ***array-key*** `$key` - The desired key
 
 ##### Return Value
 
-- ***array*** - The flattened array
+- ***array<array-key,mixed>*** - The flattened array
 
 Given an array of similarly keyed arrays, returns an array of only the values of the key.
 
@@ -80,12 +80,12 @@ function array_keys_array(array $arrays, $keys)
 
 ##### Parameters
 
-- ***array*** `$arrays` - An array of similarly keyed arrays
-- ***array*** | ***int*** | ***string*** `$keys` - The key or array of keys to return
+- ***array<array-key,array<array-key,mixed>>*** `$arrays` - An array of similarly keyed arrays
+- ***array-key*** | ***array<array-key,array-key>*** `$keys` - The key or array of keys to return
 
 ##### Return Value
 
-- ***array*** - The array of arrays with just the selected keys
+- ***array<array-key,array<array-key,mixed>>*** - The array of arrays with just the selected keys
 
 Given an array of similarly keyed arrays, returns an array of only the selected keys.
 
@@ -97,12 +97,12 @@ function array_key_refill(array $array, array $keys, $fill = array())
 
 ##### Parameters
 
-- ***array*** `$array` - A Keyed array
-- ***array*** `$keys` - The keys that must exist
+- ***array<array-key,mixed>*** `$array` - A Keyed array
+- ***array<array-key,array-key>*** `$keys` - The keys that must exist
 - ***mixed*** `$fill` - The desired value to fill with
 
 ##### Return Value
 
-- ***array***
+- ***array<array-key,mixed>***
 
 Given a keyed array, fills any missing values.
\ No newline at end of file
diff --git a/composer.json b/composer.json
index f566721..b9556f0 100644
--- a/composer.json
+++ b/composer.json
@@ -31,6 +31,7 @@
 	},
 	"require-dev": {
 		"donatj/mddoc": "^0.14.1",
+		"phpstan/phpstan": "=2.3.1",
 		"phpunit/phpunit": "~9|~11"
 	},
 	"autoload"   : {
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 0000000..3e639cd
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,4 @@
+parameters:
+    level: 9
+    paths:
+        - src
diff --git a/src/array.php b/src/array.php
index 82f2b8b..caecd7b 100644
--- a/src/array.php
+++ b/src/array.php
@@ -4,9 +4,9 @@
 	/**
 	 * Given an array, find all the values recursively.
 	 *
-	 * @param  array $array The Array to be Flattened
-	 * @param  bool  $allow_duplicates Should the array allow duplicates
-	 * @return array The resulting array or NULL on failure
+	 * @param  array<array-key, mixed> $array The Array to be Flattened
+	 * @param  bool                     $allow_duplicates Should the array allow duplicates
+	 * @return array<array-key, mixed> The resulting array or NULL on failure
 	 */
 	function array_flatten( array $array, $allow_duplicates = false ) {
 		$it    = new RecursiveIteratorIterator(new RecursiveArrayIterator($array));
@@ -14,8 +14,10 @@ function array_flatten( array $array, $allow_duplicates = false ) {
 		foreach( $it as $v ) {
 			if( $allow_duplicates ) {
 				$final[] = $v;
-			} else {
+			} elseif( is_int($v) || is_string($v) ) {
 				$final[$v] = $v;
+			} else {
+				$final[] = $v;
 			}
 		}
 
@@ -27,11 +29,11 @@ function array_flatten( array $array, $allow_duplicates = false ) {
 	/**
 	 * Given an array of arrays, merges the array's children together.
 	 *
-	 * @param array      $arrays An array of arrays.
-	 * @param array|null $keys The merged array.
-	 * @return array The resulting blended array
+	 * @param array<array-key, mixed>            $arrays An array of arrays.
+	 * @param array<array-key, array-key>|null   $keys The merged array.
+	 * @return array<array-key, mixed> The resulting blended array
 	 */
-	function array_blend( array $arrays, array $keys = null ) {
+	function array_blend( array $arrays, ?array $keys = null ) {
 		$out = array();
 
 		foreach( $arrays as $key => $array ) {
@@ -50,9 +52,9 @@ function array_blend( array $arrays, array $keys = null ) {
 	/**
 	 * Given an array of similarly keyed arrays, returns an array of only the values of the key.
 	 *
-	 * @param array      $arrays An array of similarly keyed arrays
-	 * @param int|string $key The desired key
-	 * @return array The flattened array
+	 * @param array<array-key, array<array-key, mixed>> $arrays An array of similarly keyed arrays
+	 * @param array-key                                  $key The desired key
+	 * @return array<array-key, mixed> The flattened array
 	 */
 	function array_key_array( array $arrays, $key ) {
 		$out = array();
@@ -68,9 +70,9 @@ function array_key_array( array $arrays, $key ) {
 	/**
 	 * Given an array of similarly keyed arrays, returns an array of only the selected keys.
 	 *
-	 * @param array            $arrays An array of similarly keyed arrays
-	 * @param array|int|string $keys The key or array of keys to return
-	 * @return array The array of arrays with just the selected keys
+	 * @param array<array-key, array<array-key, mixed>> $arrays An array of similarly keyed arrays
+	 * @param array-key|array<array-key, array-key>     $keys The key or array of keys to return
+	 * @return array<array-key, array<array-key, mixed>> The array of arrays with just the selected keys
 	 */
 	function array_keys_array( array $arrays, $keys ) {
 		$keys = (array)$keys;
@@ -90,10 +92,10 @@ function array_keys_array( array $arrays, $keys ) {
 	/**
 	 * Given a keyed array, fills any missing values.
 	 *
-	 * @param  array $array A Keyed array
-	 * @param  array $keys The keys that must exist
+	 * @param  array<array-key, mixed> $array A Keyed array
+	 * @param  array<array-key, array-key> $keys The keys that must exist
 	 * @param  mixed $fill The desired value to fill with
-	 * @return array
+	 * @return array<array-key, mixed>
 	 */
 	function array_key_refill( array $array, array $keys, $fill = array() ) {
 		foreach( $keys as $key ) {
diff --git a/test/ArrayFunctionsTest.php b/test/ArrayFunctionsTest.php
index 010b236..52f3b23 100644
--- a/test/ArrayFunctionsTest.php
+++ b/test/ArrayFunctionsTest.php
@@ -34,6 +34,13 @@ public function testArrayFlatten() {
 		);
 	}
 
+	public function testArrayFlattenPreservesValuesThatCannotBeArrayKeys() {
+		$this->assertSame(
+			array( true, 1.5, null ),
+			array_values(array_flatten(array( true, 1.5, null )))
+		);
+	}
+
 	public function testArrayBlend() {
 		// Test blending arrays without specifying keys
 		$arrays = array(