diff --git a/crates/macros/src/lib.rs b/crates/macros/src/lib.rs
index e744703..2e6deaf 100644
--- a/crates/macros/src/lib.rs
+++ b/crates/macros/src/lib.rs
@@ -87,10 +87,11 @@ pub fn php_module(_: TokenStream, input: TokenStream) -> TokenStream {
 }
 
 #[proc_macro_attribute]
-pub fn php_startup(_: TokenStream, input: TokenStream) -> TokenStream {
+pub fn php_startup(args: TokenStream, input: TokenStream) -> TokenStream {
+    let args = parse_macro_input!(args as AttributeArgs);
     let input = parse_macro_input!(input as ItemFn);
 
-    match startup_function::parser(input) {
+    match startup_function::parser(Some(args), input) {
         Ok(parsed) => parsed,
         Err(e) => syn::Error::new(Span::call_site(), e).to_compile_error(),
     }
diff --git a/crates/macros/src/module.rs b/crates/macros/src/module.rs
index 9eb2df3..2c118c0 100644
--- a/crates/macros/src/module.rs
+++ b/crates/macros/src/module.rs
@@ -34,7 +34,7 @@ pub fn parser(input: ItemFn) -> Result<TokenStream> {
             fn php_module_startup() {}
         })
         .map_err(|_| anyhow!("Unable to generate PHP module startup function."))?;
-        let startup = startup_function::parser(parsed)?;
+        let startup = startup_function::parser(None, parsed)?;
 
         state = STATE.lock();
         Some(startup)
diff --git a/crates/macros/src/startup_function.rs b/crates/macros/src/startup_function.rs
index 47fcfeb..76b9877 100644
--- a/crates/macros/src/startup_function.rs
+++ b/crates/macros/src/startup_function.rs
@@ -1,13 +1,27 @@
 use std::collections::HashMap;
 
 use anyhow::{anyhow, Result};
+use darling::FromMeta;
 use proc_macro2::{Ident, Span, TokenStream};
 use quote::quote;
-use syn::{Expr, ItemFn, Signature};
+use syn::{AttributeArgs, Expr, ItemFn, Signature};
 
 use crate::{class::Class, constant::Constant, STATE};
 
-pub fn parser(input: ItemFn) -> Result<TokenStream> {
+#[derive(Default, Debug, FromMeta)]
+#[darling(default)]
+struct StartupArgs {
+    before: bool,
+}
+
+pub fn parser(args: Option<AttributeArgs>, input: ItemFn) -> Result<TokenStream> {
+    let args = if let Some(args) = args {
+        StartupArgs::from_list(&args)
+            .map_err(|e| anyhow!("Unable to parse attribute arguments: {:?}", e))?
+    } else {
+        StartupArgs::default()
+    };
+
     let ItemFn { sig, block, .. } = input;
     let Signature { ident, .. } = sig;
     let stmts = &block.stmts;
@@ -17,6 +31,11 @@ pub fn parser(input: ItemFn) -> Result<TokenStream> {
 
     let classes = build_classes(&state.classes)?;
     let constants = build_constants(&state.constants);
+    let (before, after) = if args.before {
+        (Some(quote! { internal(); }), None)
+    } else {
+        (None, Some(quote! { internal(); }))
+    };
 
     let func = quote! {
         #[doc(hidden)]
@@ -30,11 +49,10 @@ pub fn parser(input: ItemFn) -> Result<TokenStream> {
 
             ::ext_php_rs::internal::ext_php_rs_startup();
 
+            #before
             #(#classes)*
             #(#constants)*
-
-            // TODO return result?
-            internal();
+            #after
 
             0
         }
diff --git a/src/lib.rs b/src/lib.rs
index 41216a3..7d9f5b2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -518,6 +518,11 @@ pub use ext_php_rs_derive::php_class;
 /// this macro if you have registered any classes or constants when using the
 /// [`macro@php_module`] macro.
 ///
+/// The attribute accepts one optional flag -- `#[php_startup(before)]` --
+/// which forces the annotated function to be called _before_ the other classes
+/// and constants are registered. By default the annotated function is called
+/// after these classes and constants are registered.
+///
 /// # Example
 ///
 /// ```