diff --git a/fuzz/fuzz_seeds/postgres_alter_extension.sql b/fuzz/fuzz_seeds/postgres_alter_extension.sql
index 593de1f0f1..596c32be97 100644
--- a/fuzz/fuzz_seeds/postgres_alter_extension.sql
+++ b/fuzz/fuzz_seeds/postgres_alter_extension.sql
@@ -26,3 +26,4 @@ ALTER EXTENSION citext ADD ROLE role_name;
 ALTER EXTENSION citext DROP STATISTICS public.st;
 ALTER EXTENSION citext DROP SUBSCRIPTION sub;
 ALTER EXTENSION citext ADD TABLESPACE ts;
+ALTER EXTENSION citext ADD FUNCTION public.f(IN a int, text);
diff --git a/src/ast/ddl.rs b/src/ast/ddl.rs
index c1fe3cd604..830d7a8769 100644
--- a/src/ast/ddl.rs
+++ b/src/ast/ddl.rs
@@ -4946,6 +4946,8 @@ pub enum AlterExtensionMember {
     ForeignDataWrapper(Ident),
     /// `FOREIGN TABLE object_name`
     ForeignTable(ObjectName),
+    /// `FUNCTION function_name [ ( [ [ argmode ] [ argname ] argtype [, ...] ] ) ]`
+    Function(FunctionDesc),
     /// `INDEX object_name`
     Index(ObjectName),
     /// `[ PROCEDURAL ] LANGUAGE object_name`
@@ -5019,6 +5021,7 @@ impl fmt::Display for AlterExtensionMember {
                 write!(f, "FOREIGN DATA WRAPPER {name}")
             }
             AlterExtensionMember::ForeignTable(name) => write!(f, "FOREIGN TABLE {name}"),
+            AlterExtensionMember::Function(function) => write!(f, "FUNCTION {function}"),
             AlterExtensionMember::Index(name) => write!(f, "INDEX {name}"),
             AlterExtensionMember::Language { procedural, name } => {
                 if *procedural {
diff --git a/src/parser/mod.rs b/src/parser/mod.rs
index 19eec492a9..f321d18457 100644
--- a/src/parser/mod.rs
+++ b/src/parser/mod.rs
@@ -12563,6 +12563,8 @@ impl<'a> Parser<'a> {
             Ok(AlterExtensionMember::ForeignTable(
                 self.parse_object_name(false)?,
             ))
+        } else if self.parse_keyword(Keyword::FUNCTION) {
+            Ok(AlterExtensionMember::Function(self.parse_function_desc()?))
         } else if self.parse_keyword(Keyword::INDEX) {
             Ok(AlterExtensionMember::Index(self.parse_object_name(false)?))
         } else if self.parse_keywords(&[Keyword::PROCEDURAL, Keyword::LANGUAGE]) {
diff --git a/tests/sqlparser_postgres.rs b/tests/sqlparser_postgres.rs
index b8d2598472..c91c42cd90 100644
--- a/tests/sqlparser_postgres.rs
+++ b/tests/sqlparser_postgres.rs
@@ -13538,6 +13538,10 @@ fn alter_extension_member_round_trip_forms(action: &str) {
         format!("ALTER EXTENSION ext_name {action} FOREIGN DATA WRAPPER fdw"),
         format!("ALTER EXTENSION ext_name {action} FOREIGN TABLE ft"),
         format!("ALTER EXTENSION ext_name {action} FOREIGN TABLE schema.ft"),
+        format!("ALTER EXTENSION ext_name {action} FUNCTION f"),
+        format!("ALTER EXTENSION ext_name {action} FUNCTION f()"),
+        format!("ALTER EXTENSION ext_name {action} FUNCTION f(INT)"),
+        format!("ALTER EXTENSION ext_name {action} FUNCTION f(INT, TEXT)"),
         format!("ALTER EXTENSION ext_name {action} INDEX idx"),
         format!("ALTER EXTENSION ext_name {action} LANGUAGE plpgsql"),
         format!("ALTER EXTENSION ext_name {action} PROCEDURAL LANGUAGE plpgsql"),
@@ -13697,6 +13701,20 @@ fn parse_alter_extension_add_member() {
         other => panic!("unexpected statement: {other:?}"),
     }
 
+    match pg_and_generic().verified_stmt("ALTER EXTENSION ext_name ADD FUNCTION f(INT)") {
+        Statement::AlterExtension(AlterExtension {
+            operation: AlterExtensionOperation::Add(AlterExtensionMember::Function(function)),
+            ..
+        }) => {
+            assert_eq!(function.name, ObjectName::from(Ident::new("f")));
+            assert_eq!(
+                function.args,
+                Some(vec![OperateFunctionArg::unnamed(DataType::Int(None))])
+            );
+        }
+        other => panic!("unexpected statement: {other:?}"),
+    }
+
     match pg_and_generic().verified_stmt("ALTER EXTENSION ext_name ADD PROCEDURAL LANGUAGE plpgsql")
     {
         Statement::AlterExtension(AlterExtension {
@@ -13723,6 +13741,10 @@ fn parse_alter_extension_add_member() {
             "ALTER EXTENSION ext_name ADD SCHEMA a.b",
             "Expected: end of statement, found: .",
         ),
+        (
+            "ALTER EXTENSION ext_name ADD FUNCTION 1",
+            "Expected: identifier, found: 1",
+        ),
     ] {
         assert_eq!(
             pg_and_generic().parse_sql_statements(sql).unwrap_err(),