diff --git a/frb_codegen/src/binary/commands.rs b/frb_codegen/src/binary/commands.rs
index 5d95ce3896..602aded9ed 100644
--- a/frb_codegen/src/binary/commands.rs
+++ b/frb_codegen/src/binary/commands.rs
@@ -88,6 +88,10 @@ pub(crate) struct GenerateCommandArgsPrimary {
     #[arg(long)]
     pub dart_format_line_length: Option<u32>,
 
+    /// Raw header of output generated Dart code, pasted as-it-is.
+    #[arg(long)]
+    pub dart_preamble: Option<String>,
+
     /// The generated Dart enums will not have their variant names camelCased.
     #[arg(long)]
     pub no_dart_enums_style: bool,
diff --git a/frb_codegen/src/binary/commands_parser.rs b/frb_codegen/src/binary/commands_parser.rs
index 36a7b6affe..db7669d33f 100644
--- a/frb_codegen/src/binary/commands_parser.rs
+++ b/frb_codegen/src/binary/commands_parser.rs
@@ -52,6 +52,7 @@ fn compute_codegen_config_from_naive_command_args(
         rust_output: args.rust_output,
         dart_entrypoint_class_name: args.dart_entrypoint_class_name,
         dart_format_line_length: args.dart_format_line_length,
+        dart_preamble: args.dart_preamble,
         dart_enums_style: Some(!args.no_dart_enums_style),
         add_mod_to_lib: Some(!args.no_add_mod_to_lib),
         llvm_path: args.llvm_path,
diff --git a/frb_codegen/src/library/codegen/config/config.rs b/frb_codegen/src/library/codegen/config/config.rs
index 2f00a40149..85fd2104ae 100644
--- a/frb_codegen/src/library/codegen/config/config.rs
+++ b/frb_codegen/src/library/codegen/config/config.rs
@@ -15,6 +15,7 @@ pub struct Config {
     pub rust_output: Option<String>,
     pub dart_entrypoint_class_name: Option<String>,
     pub dart_format_line_length: Option<u32>,
+    pub dart_preamble: Option<String>,
     pub dart_enums_style: Option<bool>,
     pub add_mod_to_lib: Option<bool>,
     pub llvm_path: Option<Vec<String>>,
diff --git a/frb_codegen/src/library/codegen/config/internal_config_parser.rs b/frb_codegen/src/library/codegen/config/internal_config_parser.rs
index 4154e5caf5..73b14eae29 100644
--- a/frb_codegen/src/library/codegen/config/internal_config_parser.rs
+++ b/frb_codegen/src/library/codegen/config/internal_config_parser.rs
@@ -119,6 +119,7 @@ impl InternalConfig {
                     dart_entrypoint_class_name: dart_output_class_name_pack
                         .entrypoint_class_name
                         .clone(),
+                    dart_preamble: config.dart_preamble.clone().unwrap_or_default(),
                 },
                 wire: GeneratorWireInternalConfig {
                     dart: GeneratorWireDartInternalConfig {
diff --git a/frb_codegen/src/library/codegen/generator/api_dart/internal_config.rs b/frb_codegen/src/library/codegen/generator/api_dart/internal_config.rs
index 12cb0f7c02..38e688da85 100644
--- a/frb_codegen/src/library/codegen/generator/api_dart/internal_config.rs
+++ b/frb_codegen/src/library/codegen/generator/api_dart/internal_config.rs
@@ -7,4 +7,5 @@ pub(crate) struct GeneratorApiDartInternalConfig {
     pub dart3: bool,
     pub dart_decl_base_output_path: PathBuf,
     pub dart_entrypoint_class_name: String,
+    pub dart_preamble: String,
 }
diff --git a/frb_codegen/src/library/codegen/generator/api_dart/mod.rs b/frb_codegen/src/library/codegen/generator/api_dart/mod.rs
index b58353481c..3c84cf643f 100644
--- a/frb_codegen/src/library/codegen/generator/api_dart/mod.rs
+++ b/frb_codegen/src/library/codegen/generator/api_dart/mod.rs
@@ -48,21 +48,31 @@ mod tests {
     use crate::utils::logs::configure_opinionated_test_logging;
     use crate::utils::test_utils::{get_test_fixture_dir, text_golden_test};
     use serial_test::serial;
+    use std::collections::HashMap;
     use std::env;
 
     #[test]
     #[serial]
     fn test_simple() -> anyhow::Result<()> {
-        body("library/codegen/generator/api_dart/mod/simple")
+        body(
+            "library/codegen/generator/api_dart/mod/simple",
+            HashMap::from([
+                ("api.dart", "expect_output.dart"),
+                ("dep.dart", "expect_output2.dart"),
+            ]),
+        )
     }
 
     #[test]
     #[serial]
     fn test_functions() -> anyhow::Result<()> {
-        body("library/codegen/generator/api_dart/mod/functions")
+        body(
+            "library/codegen/generator/api_dart/mod/functions",
+            HashMap::from([("api.dart", "expect_output.dart")]),
+        )
     }
 
-    fn body(fixture_name: &str) -> anyhow::Result<()> {
+    fn body(fixture_name: &str, expect_outputs: HashMap<&str, &str>) -> anyhow::Result<()> {
         configure_opinionated_test_logging();
         let test_fixture_dir = get_test_fixture_dir(fixture_name);
         env::set_current_dir(&test_fixture_dir)?;
@@ -83,10 +93,13 @@ mod tests {
         )?;
 
         let output_texts = actual.output_texts;
-        assert_eq!(output_texts.0.len(), 1);
-
-        let raw_text = (output_texts.0[0].text).replace(env!("CARGO_PKG_VERSION"), "{VERSION}");
-        text_golden_test(raw_text, &test_fixture_dir.join("expect_output.dart"))?;
+        assert_eq!(output_texts.0.len(), expect_outputs.len());
+        for path_text in output_texts.0 {
+            let path = path_text.path.file_name().unwrap().to_str().unwrap();
+            let expect_output = expect_outputs.get(path).unwrap();
+            let raw_text = (path_text.text).replace(env!("CARGO_PKG_VERSION"), "{VERSION}");
+            text_golden_test(raw_text, &test_fixture_dir.join(expect_output))?;
+        }
 
         Ok(())
     }
diff --git a/frb_codegen/src/library/codegen/generator/api_dart/spec_generator/mod.rs b/frb_codegen/src/library/codegen/generator/api_dart/spec_generator/mod.rs
index 4e34035cc6..08fc97fd9b 100644
--- a/frb_codegen/src/library/codegen/generator/api_dart/spec_generator/mod.rs
+++ b/frb_codegen/src/library/codegen/generator/api_dart/spec_generator/mod.rs
@@ -40,6 +40,7 @@ pub(crate) struct ApiDartOutputSpecItem {
     pub funcs: Vec<ApiDartGeneratedFunction>,
     pub classes: Vec<ApiDartGeneratedClass>,
     pub imports: DartBasicHeaderCode,
+    pub preamble: String,
     pub unused_types: Vec<String>,
     pub needs_freezed: bool,
 }
@@ -134,6 +135,7 @@ fn generate_item(
         funcs,
         classes,
         imports,
+        preamble: context.config.dart_preamble.clone(),
         unused_types,
         needs_freezed,
     })
diff --git a/frb_codegen/src/library/codegen/generator/api_dart/text_generator.rs b/frb_codegen/src/library/codegen/generator/api_dart/text_generator.rs
index dca717eaaf..9aef083dd6 100644
--- a/frb_codegen/src/library/codegen/generator/api_dart/text_generator.rs
+++ b/frb_codegen/src/library/codegen/generator/api_dart/text_generator.rs
@@ -59,8 +59,10 @@ fn generate_end_api_text(
     // TODO use relative path calculation
     let path_frb_generated = "../".repeat(path_chunks_len - 2) + "frb_generated.dart";
 
+    let preamble = &item.preamble.as_str();
     let mut header = DartBasicHeaderCode {
         file_top: generate_code_header()
+            + if !preamble.is_empty() {"\n\n"} else {""} + preamble
             + "\n\n// ignore_for_file: invalid_use_of_internal_member, unused_import, unnecessary_import\n",
         import: format!(
             "
diff --git a/frb_codegen/src/library/codegen/generator/wire/dart/spec_generator/misc/mod.rs b/frb_codegen/src/library/codegen/generator/wire/dart/spec_generator/misc/mod.rs
index 225c104f3c..0e62402f46 100644
--- a/frb_codegen/src/library/codegen/generator/wire/dart/spec_generator/misc/mod.rs
+++ b/frb_codegen/src/library/codegen/generator/wire/dart/spec_generator/misc/mod.rs
@@ -79,7 +79,9 @@ fn generate_boilerplate(
         ..
     } = &context.config.dart_output_class_name_pack;
 
+    let dart_preamble = &context.api_dart_config.dart_preamble.as_str();
     let file_top = generate_code_header()
+        + if !dart_preamble.is_empty() {"\n\n"} else {""} + dart_preamble
         + "\n\n// ignore_for_file: unused_import, unused_element, unnecessary_import, duplicate_ignore, invalid_use_of_internal_member, annotate_overrides, non_constant_identifier_names, curly_braces_in_flow_control_structures, prefer_const_literals_to_create_immutables, unused_field\n";
 
     let mut universal_imports = generate_import_dart_api_layer(
diff --git a/frb_codegen/test_fixtures/library/codegen/config/internal_config_parser/single_rust_input/expect_output.json b/frb_codegen/test_fixtures/library/codegen/config/internal_config_parser/single_rust_input/expect_output.json
index cb7dd6f80d..3afc43a3d9 100644
--- a/frb_codegen/test_fixtures/library/codegen/config/internal_config_parser/single_rust_input/expect_output.json
+++ b/frb_codegen/test_fixtures/library/codegen/config/internal_config_parser/single_rust_input/expect_output.json
@@ -20,7 +20,8 @@
       "dart3": true,
       "dart_decl_base_output_path": "{the-working-directory}/my_dart_folder",
       "dart_entrypoint_class_name": "RustLib",
-      "dart_enums_style": true
+      "dart_enums_style": true,
+      "dart_preamble": ""
     },
     "wire": {
       "c": {
diff --git a/frb_codegen/test_fixtures/library/codegen/config/internal_config_parser/wildcard_rust_input/expect_output.json b/frb_codegen/test_fixtures/library/codegen/config/internal_config_parser/wildcard_rust_input/expect_output.json
index 27942f99b8..57ddebdf42 100644
--- a/frb_codegen/test_fixtures/library/codegen/config/internal_config_parser/wildcard_rust_input/expect_output.json
+++ b/frb_codegen/test_fixtures/library/codegen/config/internal_config_parser/wildcard_rust_input/expect_output.json
@@ -20,7 +20,8 @@
       "dart3": true,
       "dart_decl_base_output_path": "{the-working-directory}/my_dart_folder",
       "dart_entrypoint_class_name": "RustLib",
-      "dart_enums_style": true
+      "dart_enums_style": true,
+      "dart_preamble": ""
     },
     "wire": {
       "c": {
diff --git a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/expect_output.dart b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/expect_output.dart
index e630ccbfe7..820b484ef4 100644
--- a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/expect_output.dart
+++ b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/expect_output.dart
@@ -2,8 +2,11 @@
         // This file is automatically generated, so please do not edit it.
 // Generated by `flutter_rust_bridge`@ {VERSION}.
 
+// test for dart_preamble
+
 // ignore_for_file: invalid_use_of_internal_member, unused_import, unnecessary_import
 
+import 'dep.dart';
 import 'frb_generated.dart';
 import 'package:flutter_rust_bridge/flutter_rust_bridge_for_generated.dart';
 
@@ -12,5 +15,7 @@ import 'package:flutter_rust_bridge/flutter_rust_bridge_for_generated.dart';
 
         Future<void> firstFunction({dynamic hint}) => RustLib.instance.api.crateApiFirstFunction(hint: hint);
 
+Future<void> secondFunction({required Simple arg , dynamic hint}) => RustLib.instance.api.crateApiSecondFunction(arg: arg, hint: hint);
+
         
         
\ No newline at end of file
diff --git a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/expect_output2.dart b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/expect_output2.dart
new file mode 100644
index 0000000000..0a5202a7f0
--- /dev/null
+++ b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/expect_output2.dart
@@ -0,0 +1,39 @@
+
+        // This file is automatically generated, so please do not edit it.
+// Generated by `flutter_rust_bridge`@ {VERSION}.
+
+// test for dart_preamble
+
+// ignore_for_file: invalid_use_of_internal_member, unused_import, unnecessary_import
+
+import 'frb_generated.dart';
+import 'package:flutter_rust_bridge/flutter_rust_bridge_for_generated.dart';
+
+
+        
+
+        
+
+        class Simple  {
+                final int val;
+
+                const Simple({required this.val ,});
+
+                
+                
+
+                
+        @override
+        int get hashCode => val.hashCode;
+        
+
+                
+        @override
+        bool operator ==(Object other) =>
+            identical(this, other) ||
+            other is Simple &&
+                runtimeType == other.runtimeType
+                && val == other.val;
+        
+            }
+        
\ No newline at end of file
diff --git a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/flutter_rust_bridge.yaml b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/flutter_rust_bridge.yaml
index eb15b30ea2..4632478305 100644
--- a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/flutter_rust_bridge.yaml
+++ b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/flutter_rust_bridge.yaml
@@ -1,3 +1,4 @@
 rust_input: src/api.rs
 dart_output: .
 c_output: frb_generated.h
+dart_preamble: "// test for dart_preamble"
diff --git a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/api.rs b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/api.rs
index 001e0c67a3..7661af1a37 100644
--- a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/api.rs
+++ b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/api.rs
@@ -1 +1,4 @@
+use super::dep::Simple;
+
 pub fn first_function() {}
+pub fn second_function(arg: Simple) {}
diff --git a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/dep.rs b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/dep.rs
new file mode 100644
index 0000000000..f7d0d2061d
--- /dev/null
+++ b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/dep.rs
@@ -0,0 +1,3 @@
+pub struct Simple{
+  val:u32
+}
diff --git a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/lib.rs b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/lib.rs
index b32f9e29f1..baa02899c3 100644
--- a/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/lib.rs
+++ b/frb_codegen/test_fixtures/library/codegen/generator/api_dart/mod/simple/src/lib.rs
@@ -1 +1,2 @@
 mod api;
+mod dep;
diff --git a/website/docs/generated/_frb-codegen-command-generate.mdx b/website/docs/generated/_frb-codegen-command-generate.mdx
index f2b60cf716..6d96cf1e4a 100644
--- a/website/docs/generated/_frb-codegen-command-generate.mdx
+++ b/website/docs/generated/_frb-codegen-command-generate.mdx
@@ -36,6 +36,9 @@ Options:
       --dart-format-line-length <DART_FORMAT_LINE_LENGTH>
           Line length for Dart formatting
 
+      --dart-preamble <DART_PREAMBLE>
+          Raw header of output generated Dart code, pasted as-it-is
+
       --no-dart-enums-style
           The generated Dart enums will not have their variant names camelCased