diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3e1b73b..d4b1859 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@
   * `ServerNameBefore32`: detect Server Object `name` usage in pre-3.2 documents (3.2 addition)
   * `ExampleValueFieldsBefore32`: detect Example Object `dataValue` / `serializedValue` usage in pre-3.2 documents (3.2 additions)
 * validate a value against a schema without `type`: keywords such as `properties`, `required`, `items`, `maxLength`, `enum` and `minimum` now apply when the value has the type the keyword is for, as in JSON Schema. They were all skipped before, so a value that breaks them may now fail validation
+* accept a file object for array-form `type` with `format: binary` (3.1) when `coerce_value` is off, the same way as a single `type: string`
 
 ## 2.5.0 (2026-10-21)
 * add OpenAPI 3.2 `SpecValidator` rules
diff --git a/lib/openapi_parser/schema_validator.rb b/lib/openapi_parser/schema_validator.rb
index 814d4ec..69e8100 100644
--- a/lib/openapi_parser/schema_validator.rb
+++ b/lib/openapi_parser/schema_validator.rb
@@ -124,6 +124,11 @@ def validator(value, schema)
       return one_of_validator if schema.one_of
       return nil_validator if value.nil?
 
+      # 3.1: `format: binary` with `string` in an array-form `type` accepts a
+      # non-String object such as an uploaded file, the same way as a single
+      # `type: string`. The string validator skips the check for `binary`.
+      return string_validator if binary_string_in_type_array?(value, schema)
+
       # 3.1: pick the type from an Array whose primitive class matches the
       # value, then dispatch as if it were a single-type schema. If nothing
       # matches we still pick a candidate so the relevant validator emits
@@ -169,6 +174,14 @@ def validator_for_type(type)
       end
     end
 
+    # 3.1: a non-String value for an array-form `type` that lists `string`
+    # with `format: binary`, such as an uploaded file object.
+    def binary_string_in_type_array?(value, schema)
+      return false if value.is_a?(String)
+
+      schema.format == 'binary' && schema.type.is_a?(Array) && schema.type.include?('string')
+    end
+
     # 3.1: when coercing, a value whose class matches no listed type is tried
     # against each listed type, the same way a single `type` coerces it.
     # Request params arrive as Strings ("5" for `type: [integer, "null"]`),
diff --git a/spec/openapi_parser/schema_validator_spec.rb b/spec/openapi_parser/schema_validator_spec.rb
index 94ef51c..87726ae 100644
--- a/spec/openapi_parser/schema_validator_spec.rb
+++ b/spec/openapi_parser/schema_validator_spec.rb
@@ -1194,4 +1194,56 @@ class ValidatableTest
       end
     end
   end
+
+  describe 'array-form type with format: binary (3.1)' do
+    let(:options) { ::OpenAPIParser::SchemaValidator::Options.new }
+    let(:target) { { 'type' => ['string', 'null'], 'format' => 'binary' } }
+    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 an arbitrary object except String is given' do
+      it 'passes validation the same way as a single string type' do
+        value = ['b', 'i', 'n', 'a', 'r', 'y']
+        expect(OpenAPIParser::SchemaValidator.validate(value, schema, options)).to eq value
+      end
+    end
+
+    context 'when a String is given' do
+      it 'passes validation' do
+        expect(OpenAPIParser::SchemaValidator.validate('binary', schema, options)).to eq 'binary'
+      end
+    end
+
+    context 'when nil is given' do
+      it 'passes validation' do
+        expect(OpenAPIParser::SchemaValidator.validate(nil, schema, options)).to eq nil
+      end
+    end
+
+    context 'when string is not listed' do
+      let(:target) { { 'type' => ['integer', 'null'], 'format' => 'binary' } }
+
+      it 'raises a type-mismatch error' do
+        expect do
+          OpenAPIParser::SchemaValidator.validate(['b', 'i', 'n', 'a', 'r', 'y'], schema, options)
+        end.to raise_error(OpenAPIParser::ValidateError, /expected \["integer", "null"\]/)
+      end
+    end
+
+    context 'when coerce_value is on' do
+      let(:options) { ::OpenAPIParser::SchemaValidator::Options.new(coerce_value: true) }
+
+      it 'passes validation' do
+        value = ['b', 'i', 'n', 'a', 'r', 'y']
+        expect(OpenAPIParser::SchemaValidator.validate(value, schema, options)).to eq value
+      end
+    end
+  end
 end