diff --git a/CHANGELOG.md b/CHANGELOG.md
index e6785f8..583d240 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,7 @@
 * support root-level `webhooks` (OpenAPI 3.1) in the parse layer
 * support `const` (OpenAPI 3.1) with exact-equality value validation
 * support `contentSchema` (OpenAPI 3.1) in the parse layer
+* coerce String values into array-form `type` (3.1) when `coerce_value` is on, so params like `type: [integer, "null"]` accept `"5"`
 
 ## 2.3.1 (2025-11-14)
 * add optional date coercion with behavior matching existing datetime coercion
diff --git a/lib/openapi_parser/schema_validator.rb b/lib/openapi_parser/schema_validator.rb
index 7221c44..e13ca99 100644
--- a/lib/openapi_parser/schema_validator.rb
+++ b/lib/openapi_parser/schema_validator.rb
@@ -82,6 +82,8 @@ def validate_schema(value, schema, **keyword_args)
       return [nil, OpenAPIParser::ValidateError.new(value, "const #{schema.const.inspect}", schema.object_reference)] if value != schema.const
     end
 
+    return coerce_into_type_array(value, schema, **keyword_args) if coerce_into_type_array?(value, schema)
+
     if (v = validator(value, schema))
       if keyword_args.empty?
         return v.coerce_and_validate(value, schema)
@@ -124,7 +126,12 @@ def validator(value, schema)
         effective_type = matched
       end
 
-      case effective_type
+      validator_for_type(effective_type)
+    end
+
+    # @return [OpenAPIParser::SchemaValidator::Base]
+    def validator_for_type(type)
+      case type
       when 'string'
         string_validator
       when 'integer'
@@ -147,6 +154,36 @@ def validator(value, schema)
       end
     end
 
+    # 3.1: request params arrive as Strings, so `type: [integer, "null"]`
+    # never matches by class. When coercing, try each listed type instead.
+    # @return [Boolean]
+    def coerce_into_type_array?(value, schema)
+      return false unless @coerce_value && value.is_a?(String)
+      return false if schema.any_of || schema.all_of || schema.one_of
+
+      schema.type.is_a?(Array) && pick_array_type(value, schema.type).nil?
+    end
+
+    # 3.1: returns the first listed type that coerces, or the first type's error.
+    # @return [Array] coerced value and error
+    def coerce_into_type_array(value, schema, **keyword_args)
+      first_error = nil
+      (schema.type - ['null']).each do |type|
+        v = validator_for_type(type)
+        coerced, err = if keyword_args.empty?
+                         v.coerce_and_validate(value, schema)
+                       else
+                         v.coerce_and_validate(value, schema, **keyword_args)
+                       end
+        return [coerced, nil] if err.nil?
+
+        first_error ||= err
+      end
+      return [nil, first_error] if first_error
+
+      type_mismatch_validator.coerce_and_validate(value, schema)
+    end
+
     def type_mismatch_validator
       @type_mismatch_validator ||= OpenAPIParser::SchemaValidator::TypeMismatchValidator.new(self, @coerce_value)
     end
diff --git a/sig/openapi_parser/schema_validator.rbs b/sig/openapi_parser/schema_validator.rbs
index 160c999..7414480 100644
--- a/sig/openapi_parser/schema_validator.rbs
+++ b/sig/openapi_parser/schema_validator.rbs
@@ -27,6 +27,9 @@ module OpenAPIParser
 
     private
     def validator: (Object value, OpenAPIParser::Schemas::Schema schema) -> [OpenAPIParser::SchemaValidator::Base, OpenAPIParser::validate_error]
+    def validator_for_type: (String? type) -> OpenAPIParser::SchemaValidator::Base
+    def coerce_into_type_array?: (Object value, OpenAPIParser::Schemas::Schema schema) -> bool
+    def coerce_into_type_array: (Object value, OpenAPIParser::Schemas::Schema schema, **untyped) -> [Object, OpenAPIParser::validate_error]
     def string_validator: -> OpenAPIParser::SchemaValidator::StringValidator
     def integer_validator: -> OpenAPIParser::SchemaValidator::IntegerValidator
     def float_validator: -> OpenAPIParser::SchemaValidator::FloatValidator
diff --git a/spec/openapi_parser/schema_validator_spec.rb b/spec/openapi_parser/schema_validator_spec.rb
index 7b4decd..35e1b31 100644
--- a/spec/openapi_parser/schema_validator_spec.rb
+++ b/spec/openapi_parser/schema_validator_spec.rb
@@ -1108,4 +1108,66 @@ class ValidatableTest
       end
     end
   end
+
+  describe 'array-form type coercion (3.1)' do
+    let(:options) { ::OpenAPIParser::SchemaValidator::Options.new(coerce_value: true) }
+    let(:target) { { 'type' => ['integer', 'null'], 'minimum' => 0 } }
+    let(:schema) do
+      raw = {
+        'openapi' => '3.1.0',
+        'info' => { 'title' => 'test', 'version' => '1.0' },
+        'paths' => {},
+        'components' => { 'schemas' => { 'Target' => target } },
+      }
+      OpenAPIParser.parse(raw, strict_reference_validation: false).components.schemas['Target']
+    end
+
+    context 'when a String coerces into a listed type' do
+      it 'returns the coerced value' do
+        expect(OpenAPIParser::SchemaValidator.validate('5', schema, options)).to eq 5
+      end
+    end
+
+    context 'when an earlier listed type does not coerce' do
+      let(:target) { { 'type' => ['integer', 'boolean'] } }
+
+      it 'tries the next listed type' do
+        expect(OpenAPIParser::SchemaValidator.validate('true', schema, options)).to eq true
+      end
+    end
+
+    context 'when string is listed' do
+      let(:target) { { 'type' => ['integer', 'string'] } }
+
+      it 'keeps the String' do
+        expect(OpenAPIParser::SchemaValidator.validate('5', schema, options)).to eq '5'
+      end
+    end
+
+    context 'when no listed type coerces' do
+      it 'raises the first type error' do
+        expect do
+          OpenAPIParser::SchemaValidator.validate('abc', schema, options)
+        end.to raise_error(OpenAPIParser::ValidateError, /integer/)
+      end
+    end
+
+    context 'when the coerced value violates a constraint' do
+      it 'raises a validation error' do
+        expect do
+          OpenAPIParser::SchemaValidator.validate('-1', schema, options)
+        end.to raise_error(OpenAPIParser::LessThanMinimum)
+      end
+    end
+
+    context 'when coerce_value is off' do
+      let(:options) { ::OpenAPIParser::SchemaValidator::Options.new }
+
+      it 'raises a type-mismatch error' do
+        expect do
+          OpenAPIParser::SchemaValidator.validate('5', schema, options)
+        end.to raise_error(OpenAPIParser::ValidateError)
+      end
+    end
+  end
 end