diff --git a/src/tree/definition/function.rs b/src/tree/definition/function.rs
index 44b00da..4074d5b 100644
--- a/src/tree/definition/function.rs
+++ b/src/tree/definition/function.rs
@@ -507,6 +507,10 @@ impl std::fmt::Display for FunctionLikeParameterDefaultValueDefinition {
 
 impl std::fmt::Display for FunctionDefinition {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if !self.modifiers.modifiers.is_empty() {
+            write!(f, "{} ", self.modifiers)?;
+        }
+
         write!(f, "{} {}", self.function, self.name)?;
 
         if let Some(templates) = &self.templates {
@@ -598,6 +602,13 @@ mod tests {
     #[test]
     fn test_function_definition_display() {
         let function_definition = FunctionDefinition {
+            modifiers: ModifierGroupDefinition {
+                position: 0,
+                modifiers: vec![ModifierDefinition::Async(Keyword::new(
+                    ByteString::from("async"),
+                    0,
+                ))],
+            },
             function: Keyword::new(ByteString::from("function"), 0),
             name: Identifier {
                 position: 0,
@@ -646,7 +657,7 @@ mod tests {
 
         assert_eq!(
             function_definition.to_string(),
-            "function Foo(i32 $foo): i64 { /* ... */ }"
+            "async function Foo(i32 $foo): i64 { /* ... */ }"
         );
     }
 
diff --git a/src/tree/expression/function.rs b/src/tree/expression/function.rs
index ee2c042..c93ba96 100644
--- a/src/tree/expression/function.rs
+++ b/src/tree/expression/function.rs
@@ -195,9 +195,10 @@ impl Node for AnonymousFunctionUseClauseVariableExpression {
 
 impl std::fmt::Display for ArrowFunctionExpression {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        if let Some(r#static) = &self.r#static {
-            write!(f, "{} ", r#static)?;
+        if !self.modifiers.modifiers.is_empty() {
+            write!(f, "{} ", self.modifiers)?;
         }
+
         write!(
             f,
             "{} {}{} => {};",
@@ -208,9 +209,10 @@ impl std::fmt::Display for ArrowFunctionExpression {
 
 impl std::fmt::Display for AnonymousFunctionExpression {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        if let Some(r#static) = &self.r#static {
-            write!(f, "{} ", r#static)?;
+        if !self.modifiers.modifiers.is_empty() {
+            write!(f, "{} ", self.modifiers)?;
         }
+
         write!(f, "{} {}", self.function, self.parameters)?;
 
         if let Some(use_clause) = &self.use_clause {
@@ -238,6 +240,7 @@ mod tests {
     use super::*;
     use crate::lexer::byte_string::ByteString;
     use crate::tree::definition::function::FunctionLikeParameterDefinition;
+    use crate::tree::definition::modifier::ModifierDefinition;
     use crate::tree::definition::r#type::SignedIntegerTypeDefinition;
     use crate::tree::definition::r#type::TypeDefinition;
 
@@ -246,7 +249,13 @@ mod tests {
         let arrow_function_expression = ArrowFunctionExpression {
             attributes: vec![],
             comments: CommentGroup { comments: vec![] },
-            r#static: Some(Keyword::new(ByteString::from("static"), 0)),
+            modifiers: ModifierGroupDefinition {
+                position: 0,
+                modifiers: vec![ModifierDefinition::Static(Keyword::new(
+                    ByteString::from("static"),
+                    0,
+                ))],
+            },
             r#fn: Keyword::new(ByteString::from("fn"), 0),
             parameters: FunctionLikeParameterListDefinition {
                 comments: CommentGroup { comments: vec![] },
@@ -296,7 +305,13 @@ mod tests {
         let anonymous_function_expression = AnonymousFunctionExpression {
             attributes: vec![],
             comments: CommentGroup { comments: vec![] },
-            r#static: Some(Keyword::new(ByteString::from("static"), 0)),
+            modifiers: ModifierGroupDefinition {
+                position: 0,
+                modifiers: vec![ModifierDefinition::Static(Keyword::new(
+                    ByteString::from("static"),
+                    0,
+                ))],
+            },
             function: Keyword::new(ByteString::from("function"), 0),
             parameters: FunctionLikeParameterListDefinition {
                 comments: CommentGroup { comments: vec![] },
diff --git a/tests/samples/0111/tree.txt b/tests/samples/0111/tree.txt
index c682818..917662c 100644
--- a/tests/samples/0111/tree.txt
+++ b/tests/samples/0111/tree.txt
@@ -2,10 +2,14 @@ DefinitionTree {
     definitions: [
         Function(
             FunctionDefinition {
+                attributes: [],
                 comments: CommentGroup {
                     comments: [],
                 },
-                attributes: [],
+                modifiers: ModifierGroupDefinition {
+                    position: 0,
+                    modifiers: [],
+                },
                 function: Keyword {
                     value: "function",
                     position: 0,
diff --git a/tests/samples/0112/tree.txt b/tests/samples/0112/tree.txt
index dfaf090..8035fc5 100644
--- a/tests/samples/0112/tree.txt
+++ b/tests/samples/0112/tree.txt
@@ -2,10 +2,14 @@ DefinitionTree {
     definitions: [
         Function(
             FunctionDefinition {
+                attributes: [],
                 comments: CommentGroup {
                     comments: [],
                 },
-                attributes: [],
+                modifiers: ModifierGroupDefinition {
+                    position: 0,
+                    modifiers: [],
+                },
                 function: Keyword {
                     value: "function",
                     position: 0,
diff --git a/tests/samples/0113/tree.txt b/tests/samples/0113/tree.txt
index f5b8098..0aa830c 100644
--- a/tests/samples/0113/tree.txt
+++ b/tests/samples/0113/tree.txt
@@ -2,10 +2,14 @@ DefinitionTree {
     definitions: [
         Function(
             FunctionDefinition {
+                attributes: [],
                 comments: CommentGroup {
                     comments: [],
                 },
-                attributes: [],
+                modifiers: ModifierGroupDefinition {
+                    position: 0,
+                    modifiers: [],
+                },
                 function: Keyword {
                     value: "function",
                     position: 0,
diff --git a/tests/samples/0114/tree.txt b/tests/samples/0114/tree.txt
index f7eb29f..6eb403b 100644
--- a/tests/samples/0114/tree.txt
+++ b/tests/samples/0114/tree.txt
@@ -2,10 +2,14 @@ DefinitionTree {
     definitions: [
         Function(
             FunctionDefinition {
+                attributes: [],
                 comments: CommentGroup {
                     comments: [],
                 },
-                attributes: [],
+                modifiers: ModifierGroupDefinition {
+                    position: 0,
+                    modifiers: [],
+                },
                 function: Keyword {
                     value: "function",
                     position: 0,
diff --git a/tests/samples/0115/tree.txt b/tests/samples/0115/tree.txt
index 171eafb..e1cd525 100644
--- a/tests/samples/0115/tree.txt
+++ b/tests/samples/0115/tree.txt
@@ -2,10 +2,14 @@ DefinitionTree {
     definitions: [
         Function(
             FunctionDefinition {
+                attributes: [],
                 comments: CommentGroup {
                     comments: [],
                 },
-                attributes: [],
+                modifiers: ModifierGroupDefinition {
+                    position: 0,
+                    modifiers: [],
+                },
                 function: Keyword {
                     value: "function",
                     position: 0,