diff --git a/src/ast.rs b/src/ast.rs
index 6bc68cc..e51559e 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -17,6 +17,16 @@ pub enum TypeKind {
     Record,
 }
 
+/// Represents the function argument type.
+#[derive(PartialEq, Debug, Clone)]
+pub struct FunctionArg {
+    /// A function argument name.
+    pub name: String,
+
+    /// A function argument type.
+    pub ty: InterfaceType,
+}
+
 /// Represents a type.
 #[derive(PartialEq, Debug, Clone)]
 pub enum Type {
@@ -26,15 +36,8 @@ pub enum Type {
     /// (@interface type (func (param i32 i32) (result string)))
     /// ```
     Function {
-        /// Name of a function.
-        name: String,
-
-        /// Types for the parameters (`(param …)`).
-        arg_types: Vec<InterfaceType>,
-
-        /// Name of function argument types.
-        // TODO: introduce a struct combines name and type of a field
-        arg_names: Vec<String>,
+        /// Types for the parameters (`(param (name i32))`).
+        arguments: Vec<FunctionArg>,
 
         /// Types for the results (`(result …)`).
         output_types: Vec<InterfaceType>,
diff --git a/src/decoders/binary.rs b/src/decoders/binary.rs
index 5fc6216..ba08660 100644
--- a/src/decoders/binary.rs
+++ b/src/decoders/binary.rs
@@ -77,16 +77,23 @@ fn record_field<'input, E: ParseError<&'input [u8]>>(
         return Err(Err::Error(make_error(input, ErrorKind::Eof)));
     }
 
-    consume!((input, name) = string(input)?);
+    consume!((input, name) = owned_string(input)?);
     consume!((input, ty) = ty(input)?);
 
-    Ok((
-        input,
-        RecordFieldType {
-            name: name.to_owned(),
-            ty,
-        },
-    ))
+    Ok((input, RecordFieldType { name, ty }))
+}
+
+fn function_arg<'input, E: ParseError<&'input [u8]>>(
+    mut input: &'input [u8],
+) -> IResult<&'input [u8], FunctionArg, E> {
+    if input.is_empty() {
+        return Err(Err::Error(make_error(input, ErrorKind::Eof)));
+    }
+
+    consume!((input, name) = owned_string(input)?);
+    consume!((input, ty) = ty(input)?);
+
+    Ok((input, FunctionArg { name, ty }))
 }
 
 /// Parse an interface type.
@@ -116,9 +123,9 @@ fn ty<'input, E: ParseError<&'input [u8]>>(
         0x0c => InterfaceType::I32,
         0x0d => InterfaceType::I64,
         0x0e => {
-            consume!((input, record_name) = string(input)?);
+            consume!((input, record_name) = owned_string(input)?);
 
-            InterfaceType::Record(record_name.to_owned())
+            InterfaceType::Record(record_name)
         }
         _ => return Err(Err::Error(make_error(input, ErrorKind::ParseTo))),
     };
@@ -132,13 +139,13 @@ fn record_type<'input, E: ParseError<&'input [u8]>>(
 ) -> IResult<&'input [u8], RecordType, E> {
     use crate::vec1::Vec1;
 
-    let (output, name) = string(input)?;
+    let (output, name) = owned_string(input)?;
     let (output, fields) = list(output, record_field)?;
 
     Ok((
         output,
         RecordType {
-            name: name.to_owned(),
+            name,
             fields: Vec1::new(fields).expect("Record must have at least one field, zero given."),
         },
     ))
@@ -352,15 +359,11 @@ fn types<'input, E: ParseError<&'input [u8]>>(
 
         match type_kind {
             TypeKind::Function => {
-                consume!((input, name) = string(input)?);
-                consume!((input, arg_types) = list(input, ty)?);
-                consume!((input, arg_names) = list(input, owned_string)?);
+                consume!((input, arguments) = list(input, function_arg)?);
                 consume!((input, output_types) = list(input, ty)?);
 
                 types.push(Type::Function {
-                    name: String::from(name),
-                    arg_types,
-                    arg_names,
+                    arguments,
                     output_types,
                 });
             }
diff --git a/src/decoders/wat.rs b/src/decoders/wat.rs
index 5de4da8..19d202d 100644
--- a/src/decoders/wat.rs
+++ b/src/decoders/wat.rs
@@ -416,7 +416,7 @@ impl Parse<'_> for AtInterface {
 
 #[derive(PartialEq, Debug)]
 enum FunctionType {
-    Header(String, Vec<String>, Vec<InterfaceType>),
+    Header(Vec<FunctionArg>),
     Output(Vec<InterfaceType>),
 }
 
@@ -427,17 +427,19 @@ impl Parse<'_> for FunctionType {
 
             if lookahead.peek::<keyword::param>() {
                 parser.parse::<keyword::param>()?;
-                let func_name = parser.parse()?;
 
-                let mut names = vec![];
-                let mut types = vec![];
+                let mut arguments = vec![];
 
                 while !parser.is_empty() {
-                    names.push(parser.parse()?);
-                    types.push(parser.parse()?);
+                    let arg_name: String = parser.parse()?;
+                    let arg_type: InterfaceType = parser.parse()?;
+                    arguments.push(FunctionArg {
+                        name: arg_name,
+                        ty: arg_type,
+                    });
                 }
 
-                Ok(FunctionType::Header(func_name, names, types))
+                Ok(FunctionType::Header(arguments))
             } else if lookahead.peek::<keyword::result>() {
                 parser.parse::<keyword::result>()?;
 
@@ -504,38 +506,22 @@ impl<'a> Parse<'a> for Type {
             if lookahead.peek::<keyword::func>() {
                 parser.parse::<keyword::func>()?;
 
-                let mut arg_types = vec![];
-                let mut arg_names = vec![];
+                let mut arguments = vec![];
                 let mut output_types = vec![];
-                let mut name: Option<String> = None;
 
                 while !parser.is_empty() {
                     let function_type = parser.parse::<FunctionType>()?;
 
                     match function_type {
-                        FunctionType::Header(func_name, mut names, mut types) => {
-                            name = Some(func_name);
-                            arg_names.append(&mut names);
-                            arg_types.append(&mut types);
-                        },
+                        FunctionType::Header(mut func_arguments) => {
+                            arguments.append(&mut func_arguments);
+                        }
                         FunctionType::Output(mut outputs) => output_types.append(&mut outputs),
                     }
                 }
 
-                if name.is_none() {
-                    return Err(parser.error("Malformed wast: function doesn't contain name"));
-                }
-
-                if arg_types.len() != arg_names.len() {
-                    return Err(parser.error("Malformed wast: function argument types count should be equal to argument names count"));
-                }
-
-                // It's has been already checked for None.
-                let name = name.unwrap();
                 Ok(Type::Function {
-                    name,
-                    arg_types,
-                    arg_names,
+                    arguments,
                     output_types,
                 })
             } else if lookahead.peek::<keyword::record>() {
diff --git a/src/encoders/binary.rs b/src/encoders/binary.rs
index e4d4081..7fb8f7f 100644
--- a/src/encoders/binary.rs
+++ b/src/encoders/binary.rs
@@ -186,6 +186,16 @@ where
     }
 }
 
+impl<W> ToBytes<W> for FunctionArg
+where
+    W: Write,
+{
+    fn to_bytes(&self, writer: &mut W) -> io::Result<()> {
+        self.name.to_bytes(writer)?;
+        self.ty.to_bytes(writer)
+    }
+}
+
 /// Encode a `Type` into bytes.
 ///
 /// Decoder is in `decoders::binary::types`.
@@ -196,15 +206,11 @@ where
     fn to_bytes(&self, writer: &mut W) -> io::Result<()> {
         match self {
             Type::Function {
-                name,
-                arg_types,
-                arg_names,
+                arguments,
                 output_types,
             } => {
                 TypeKind::Function.to_bytes(writer)?;
-                name.to_bytes(writer)?;
-                arg_types.to_bytes(writer)?;
-                arg_names.to_bytes(writer)?;
+                arguments.to_bytes(writer)?;
                 output_types.to_bytes(writer)?;
             }
 
diff --git a/src/encoders/wat.rs b/src/encoders/wat.rs
index a2d98a5..b566663 100644
--- a/src/encoders/wat.rs
+++ b/src/encoders/wat.rs
@@ -165,16 +165,16 @@ impl ToString for &Instruction {
 
 /// Encode a list of `InterfaceType` representing inputs into a
 /// string.
-fn encode_arguments(arg_types: &[InterfaceType], arg_names: &[String]) -> String {
+fn encode_function_arguments(arguments: &[FunctionArg]) -> String {
     // here we know that arg_names and arg_types have the same length
-    if arg_names.is_empty() {
+    if arguments.is_empty() {
         String::from("")
     } else {
         format!(
             "\n  (param{})",
-            arg_names.iter().zip(arg_types.iter()).fold(
+            arguments.iter().fold(
                 String::new(),
-                |mut accumulator, (name, ty)| {
+                |mut accumulator, FunctionArg { name, ty }| {
                     accumulator.push(' ');
                     accumulator.push_str(name);
                     accumulator.push_str(": ");
@@ -210,14 +210,11 @@ impl<'input> ToString for &Type {
     fn to_string(&self) -> String {
         match self {
             Type::Function {
-                name,
-                arg_types,
-                arg_names,
+                arguments,
                 output_types,
             } => format!(
-                r#"(@interface type (func {name} {args}{output_types}))"#,
-                name = name,
-                args = encode_arguments(arg_types, arg_names),
+                r#"(@interface type (func {args} {output_types}))"#,
+                args = encode_function_arguments(arguments),
                 output_types = output_types_to_result(&output_types),
             ),