diff --git a/src/Type/TypeInfoTypeResolver.php b/src/Type/TypeInfoTypeResolver.php
index 950a8a180..146346182 100644
--- a/src/Type/TypeInfoTypeResolver.php
+++ b/src/Type/TypeInfoTypeResolver.php
@@ -10,6 +10,7 @@
 use OpenApi\Annotations as OA;
 use OpenApi\Context;
 use OpenApi\Generator;
+use OpenApi\TypeResolverInterface;
 use PHPStan\PhpDocParser\Ast\PhpDoc\ParamTagValueNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\ReturnTagValueNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\VarTagValueNode;
@@ -32,7 +33,6 @@
 use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\TypeInfo\Type\UnionType;
 use Symfony\Component\TypeInfo\TypeContext\TypeContextFactory;
-use Symfony\Component\TypeInfo\TypeIdentifier;
 use Symfony\Component\TypeInfo\TypeResolver\ReflectionTypeResolver;
 
 class TypeInfoTypeResolver extends AbstractTypeResolver
@@ -93,7 +93,11 @@ protected function setSchemaType(OA\Schema $schema, Type $type, Analysis $analys
 
                 if ($type instanceof UnionType) {
                     if ($allBuiltin) {
-                        $schema->type = array_map(static fn (Type $t): string => (string) $t, $types);
+                        $mappableTypes = array_values(array_filter(
+                            array_map(static fn (Type $t): string => (string) $t, $types),
+                            $this->hasOpenApiType(...),
+                        ));
+                        $schema->type = [] === $mappableTypes ? Generator::UNDEFINED : $mappableTypes;
                     } else {
                         $builtinTypes = array_filter($types, static fn (Type $t): bool => $t instanceof BuiltinType);
                         $otherTypes = array_filter($types, static fn (Type $t): bool => !$t instanceof BuiltinType);
@@ -140,7 +144,7 @@ protected function setSchemaType(OA\Schema $schema, Type $type, Analysis $analys
             }
         } else {
             if ($type instanceof BuiltinType) {
-                if (!$type->isIdentifiedBy(TypeIdentifier::MIXED)) {
+                if ($this->hasOpenApiType((string) $type)) {
                     $schema->type = (string) $type;
                 }
             } elseif ($type instanceof ObjectType) {
@@ -190,6 +194,23 @@ protected function setSchemaType(OA\Schema $schema, Type $type, Analysis $analys
         return $schema;
     }
 
+    /**
+     * Checks that the given type has an OpenAPI representation.
+     *
+     * Types such as mixed, callable, resource and iterable have none; callers leave the schema open for those instead of emitting an invalid type.
+     */
+    protected function hasOpenApiType(string $native): bool
+    {
+        $native = strtolower($native);
+
+        // NATIVE_TYPE_MAP maps "mixed" to "mixed", which is not a valid OpenAPI type, so mixed has no representation.
+        if ('mixed' === $native) {
+            return false;
+        }
+
+        return 'null' === $native || array_key_exists($native, TypeResolverInterface::NATIVE_TYPE_MAP);
+    }
+
     /**645 1050272  02 1268 0026220 00
      * @param \ReflectionParameter|\ReflectionProperty|\ReflectionMethod $reflector
      */
diff --git a/tests/Fixtures/PHP/DocblockAndTypehintTypes.php b/tests/Fixtures/PHP/DocblockAndTypehintTypes.php
index 7cf908f09..bc516566a 100644
--- a/tests/Fixtures/PHP/DocblockAndTypehintTypes.php
+++ b/tests/Fixtures/PHP/DocblockAndTypehintTypes.php
@@ -137,6 +137,18 @@ class DocblockAndTypehintTypes
     #[OAT\Property]
     public array $intKeyedMap;
 
+    /**
+     * @var list<callable>
+     */
+    #[OAT\Property]
+    public array $unmappableList;
+
+    /**
+     * @var array<string, callable>
+     */
+    #[OAT\Property]
+    public array $unmappableMap;
+
     /**
      * @var int|string
      */
diff --git a/tests/Fixtures/TypedProperties.php b/tests/Fixtures/TypedProperties.php
index 66f676ffc..977179d90 100644
--- a/tests/Fixtures/TypedProperties.php
+++ b/tests/Fixtures/TypedProperties.php
@@ -8,7 +8,7 @@
 
 use OpenApi\Attributes as OAT;
 
-#[OAT\Schema()]
+#[OAT\Schema]
 class TypedProperties
 {
     #[OAT\Property]
@@ -90,4 +90,26 @@ class TypedProperties
      */
     #[OAT\Property]
     public array $stringMap;
+
+    /**
+     * A map whose value type has no OpenAPI representation.
+     *
+     * @var array<string, callable>
+     */
+    #[OAT\Property]
+    public array $unmappableMap;
+
+    /**
+     * A map whose value type is mixed, which has no OpenAPI representation.
+     *
+     * @var array<string, mixed>
+     */
+    #[OAT\Property]
+    public array $mixedMap;
+
+    /**
+     * A mixed value, which has no concrete OpenAPI type and stays an open "any value" schema.
+     */
+    #[OAT\Property]
+    public mixed $mixedValue;
 }
diff --git a/tests/Processors/AugmentPropertiesTest.php b/tests/Processors/AugmentPropertiesTest.php
index d4f4b9518..35da65ba2 100644
--- a/tests/Processors/AugmentPropertiesTest.php
+++ b/tests/Processors/AugmentPropertiesTest.php
@@ -178,6 +178,9 @@ public function testTypedProperties(): void
             $staticNullableString,
             $nativeArray,
             $stringMap,
+            $unmappableMap,
+            $mixedMap,
+            $mixedValue,
         ] = $analysis->openapi->components->schemas[0]->properties;
 
         $this->assertName($stringType, [
@@ -260,6 +263,18 @@ public function testTypedProperties(): void
             'property' => Generator::UNDEFINED,
             'type' => Generator::UNDEFINED,
         ]);
+        $this->assertName($unmappableMap, [
+            'property' => Generator::UNDEFINED,
+            'type' => Generator::UNDEFINED,
+        ]);
+        $this->assertName($mixedMap, [
+            'property' => Generator::UNDEFINED,
+            'type' => Generator::UNDEFINED,
+        ]);
+        $this->assertName($mixedValue, [
+            'property' => Generator::UNDEFINED,
+            'type' => Generator::UNDEFINED,
+        ]);
 
         $this->processorPipeline([new AugmentProperties()])->process($analysis);
 
@@ -360,6 +375,34 @@ public function testTypedProperties(): void
         $this->assertFalse(Generator::isDefault($stringMap->additionalProperties));
         $this->assertSame('string', $stringMap->additionalProperties->type);
         $this->assertTrue(Generator::isDefault($stringMap->items));
+
+        $this->assertName($unmappableMap, [
+            'property' => 'unmappableMap',
+            'type' => 'object',
+        ]);
+        $this->assertFalse(Generator::isDefault($unmappableMap->additionalProperties));
+        $this->assertTrue(
+            Generator::isDefault($unmappableMap->additionalProperties->type),
+            'callable has no OpenAPI representation, so additionalProperties stays open instead of emitting type: callable',
+        );
+
+        $this->assertName($mixedMap, [
+            'property' => 'mixedMap',
+            'type' => 'object',
+        ]);
+        $this->assertFalse(Generator::isDefault($mixedMap->additionalProperties));
+        $this->assertTrue(
+            Generator::isDefault($mixedMap->additionalProperties->type),
+            'mixed has no OpenAPI representation, so additionalProperties stays open instead of emitting type: mixed',
+        );
+
+        $this->assertName($mixedValue, [
+            'property' => 'mixedValue',
+        ]);
+        $this->assertTrue(
+            Generator::isDefault($mixedValue->type),
+            'mixed is the OpenAPI any value, so the property stays an open schema with no type instead of emitting type: mixed',
+        );
     }
 
     public function testComplexVarTypeDescription(): void
diff --git a/tests/Type/TypeResolverTest.php b/tests/Type/TypeResolverTest.php
index ac9822390..68fbf923e 100644
--- a/tests/Type/TypeResolverTest.php
+++ b/tests/Type/TypeResolverTest.php
@@ -49,6 +49,8 @@ public static function resolverAugmentCases(): iterable
                 'type-info:stringmap' => '{ "type": "object", "additionalProperties": { "type": "string" }, "property": "stringMap" }',
                 'legacy:intkeyedmap' => '{ "type": "array", "items": {}, "property": "intKeyedMap" }',
                 'type-info:intkeyedmap' => '{ "type": "object", "additionalProperties": { "type": "string" }, "property": "intKeyedMap" }',
+                'type-info:unmappablelist' => '{ "type": "array", "items": {}, "property": "unmappableList" }',
+                'type-info:unmappablemap' => '{ "type": "object", "additionalProperties": {}, "property": "unmappableMap" }',
                 'uniontype' => '{ "property": "unionType" }',
                 'promotedstring' => '{ "type": "string", "property": "promotedString" }',
                 'legacy:mixedunion' => '{ "example": "My value", "property": "mixedUnion" }',
@@ -98,6 +100,8 @@ public static function resolverAugmentCases(): iterable
                 'type-info:stringmap' => '{ "type": "object", "additionalProperties": { "type": "string" }, "property": "stringMap" }',
                 'legacy:intkeyedmap' => '{ "type": "array", "items": {}, "property": "intKeyedMap" }',
                 'type-info:intkeyedmap' => '{ "type": "object", "additionalProperties": { "type": "string" }, "property": "intKeyedMap" }',
+                'type-info:unmappablelist' => '{ "type": "array", "items": {}, "property": "unmappableList" }',
+                'type-info:unmappablemap' => '{ "type": "object", "additionalProperties": {}, "property": "unmappableMap" }',
                 'legacy:uniontype' => '{ "property": "unionType" }',
                 'type-info:uniontype' => '{ "type": [ "integer", "string" ], "property": "unionType" }',
                 'promotedstring' => '{ "type": "string", "property": "promotedString" }',