diff --git a/src/engine.rs b/src/engine.rs
index 79864466..abe08f76 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -898,8 +898,6 @@ impl<'x, 'px, 'pt> EvalContext<'_, 'x, 'px, '_, '_, '_, '_, 'pt> {
 /// # }
 /// ```
 pub struct Engine {
-    /// A module containing all functions directly loaded into the Engine.
-    pub(crate) global_namespace: Module,
     /// A collection of all modules loaded into the global namespace of the Engine.
     pub(crate) global_modules: StaticVec<Shared<Module>>,
     /// A collection of all sub-modules directly loaded into the Engine.
@@ -1034,7 +1032,6 @@ impl Engine {
     #[must_use]
     pub fn new_raw() -> Self {
         let mut engine = Self {
-            global_namespace: Default::default(),
             global_modules: Default::default(),
             global_sub_modules: Default::default(),
 
@@ -1061,7 +1058,10 @@ impl Engine {
             limits: Default::default(),
         };
 
-        engine.global_namespace.internal = true;
+        // Add the global namespace module
+        let mut global_namespace = Module::new();
+        global_namespace.internal = true;
+        engine.global_modules.push(global_namespace.into());
 
         engine
     }
@@ -2618,13 +2618,9 @@ impl Engine {
                 // 3) Imported modules - functions marked with global namespace
                 // 4) Global sub-modules - functions marked with global namespace
                 let func = self
-                    .global_namespace
-                    .get_iter(iter_type)
-                    .or_else(|| {
-                        self.global_modules
-                            .iter()
-                            .find_map(|m| m.get_iter(iter_type))
-                    })
+                    .global_modules
+                    .iter()
+                    .find_map(|m| m.get_iter(iter_type))
                     .or_else(|| mods.get_iter(iter_type))
                     .or_else(|| {
                         self.global_sub_modules
diff --git a/src/engine_api.rs b/src/engine_api.rs
index cca1d706..8e6175b0 100644
--- a/src/engine_api.rs
+++ b/src/engine_api.rs
@@ -22,6 +22,16 @@ use crate::Array;
 use crate::Map;
 
 impl Engine {
+    /// Get the global namespace module (which is the last module in `global_modules`).
+    #[inline(always)]
+    fn global_namespace(&mut self) -> &mut Module {
+        Shared::get_mut(
+            self.global_modules
+                .last_mut()
+                .expect("global_modules contains at least one module"),
+        )
+        .expect("global namespace module is never shared")
+    }
     /// Register a custom function with the [`Engine`].
     ///
     /// # Example
@@ -74,7 +84,7 @@ impl Engine {
         #[cfg(not(feature = "metadata"))]
         let param_type_names: Option<[&str; 0]> = None;
 
-        self.global_namespace.set_fn(
+        self.global_namespace().set_fn(
             name,
             FnNamespace::Global,
             FnAccess::Public,
@@ -132,7 +142,7 @@ impl Engine {
         #[cfg(not(feature = "metadata"))]
         let param_type_names: Option<[&str; 0]> = None;
 
-        self.global_namespace.set_fn(
+        self.global_namespace().set_fn(
             name,
             FnNamespace::Global,
             FnAccess::Public,
@@ -171,7 +181,7 @@ impl Engine {
         N: AsRef<str> + Into<Identifier>,
         T: Variant + Clone,
     {
-        self.global_namespace.set_raw_fn(
+        self.global_namespace().set_raw_fn(
             name,
             FnNamespace::Global,
             FnAccess::Public,
@@ -275,7 +285,7 @@ impl Engine {
         T: Variant + Clone + IntoIterator,
         <T as IntoIterator>::Item: Variant + Clone,
     {
-        self.global_namespace.set_iterable::<T>();
+        self.global_namespace().set_iterable::<T>();
         self
     }
     /// Register a getter function for a member of a registered type with the [`Engine`].
diff --git a/src/fn_call.rs b/src/fn_call.rs
index ec049173..a3e97465 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -198,12 +198,6 @@ impl Engine {
                                 source: m.id_raw().cloned(),
                             })
                         })
-                        .or_else(|| {
-                            self.global_namespace
-                                .get_fn(hash)
-                                .cloned()
-                                .map(|func| FnResolutionCacheEntry { func, source: None })
-                        })
                         .or_else(|| {
                             self.global_modules.iter().find_map(|m| {
                                 m.get_fn(hash).cloned().map(|func| FnResolutionCacheEntry {
@@ -619,8 +613,6 @@ impl Engine {
 
         // First check script-defined functions
         let result = lib.iter().any(|&m| m.contains_fn(hash_script))
-            // Then check registered functions
-            || self.global_namespace.contains_fn(hash_script)
             // Then check packages
             || self.global_modules.iter().any(|m| m.contains_fn(hash_script))
             // Then check imported modules
diff --git a/src/optimize.rs b/src/optimize.rs
index 5225eb61..32c90183 100644
--- a/src/optimize.rs
+++ b/src/optimize.rs
@@ -148,10 +148,8 @@ impl<'a> OptimizerState<'a> {
         let hash_params = calc_fn_params_hash(arg_types.iter().cloned());
         let hash = combine_hashes(hash_script, hash_params);
 
-        // First check registered functions
-        self.engine.global_namespace.contains_fn(hash)
-            // Then check packages
-            || self.engine.global_modules.iter().any(|m| m.contains_fn(hash))
+        // First  check packages
+        self.engine.global_modules.iter().any(|m| m.contains_fn(hash))
             // Then check sub-modules
             || self.engine.global_sub_modules.values().any(|m| m.contains_qualified_fn(hash))
     }