diff --git a/src/fn_call.rs b/src/fn_call.rs
index ca1aef51..6672d746 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -36,6 +36,7 @@ use crate::engine::{Map, Target, FN_GET, FN_SET};
 use crate::stdlib::{
     any::{type_name, TypeId},
     boxed::Box,
+    collections::HashSet,
     convert::TryFrom,
     format,
     iter::{empty, once},
@@ -109,22 +110,20 @@ fn restore_first_arg<'a>(old_this_ptr: Option<&'a mut Dynamic>, args: &mut FnCal
 // Add captured variables into scope
 #[cfg(not(feature = "no_capture"))]
 fn add_captured_variables_into_scope<'s>(
-    externals: &[String],
-    captured: &'s Scope<'s>,
+    externals: &HashSet<String>,
+    captured: Scope<'s>,
     scope: &mut Scope<'s>,
 ) {
-    externals
-        .iter()
-        .map(|var_name| captured.get_entry(var_name))
-        .filter(Option::is_some)
-        .map(Option::unwrap)
+    captured
+        .into_iter()
+        .filter(|ScopeEntry { name, .. }| externals.contains(name.as_ref()))
         .for_each(
             |ScopeEntry {
                  name, typ, value, ..
              }| {
                 match typ {
-                    ScopeEntryType::Normal => scope.push(name.clone(), value.clone()),
-                    ScopeEntryType::Constant => scope.push_constant(name.clone(), value.clone()),
+                    ScopeEntryType::Normal => scope.push(name, value),
+                    ScopeEntryType::Constant => scope.push_constant(name, value),
                 };
             },
         );
@@ -451,7 +450,7 @@ impl Engine {
 
                 // Add captured variables into scope
                 #[cfg(not(feature = "no_capture"))]
-                if let Some(captured) = &capture {
+                if let Some(captured) = capture {
                     add_captured_variables_into_scope(&func.externals, captured, scope);
                 }
 
@@ -801,7 +800,7 @@ impl Engine {
         let mut args: StaticVec<_>;
         let mut is_ref = false;
         let capture = if capture && !scope.is_empty() {
-            Some(scope.clone())
+            Some(scope.flatten_clone())
         } else {
             None
         };
@@ -875,7 +874,7 @@ impl Engine {
 
         #[cfg(not(feature = "no_capture"))]
         let capture = if capture && !scope.is_empty() {
-            Some(scope.clone())
+            Some(scope.flatten_clone())
         } else {
             None
         };
@@ -952,7 +951,7 @@ impl Engine {
 
                 // Add captured variables into scope
                 #[cfg(not(feature = "no_capture"))]
-                if let Some(captured) = &capture {
+                if let Some(captured) = capture {
                     add_captured_variables_into_scope(&func.externals, captured, scope);
                 }
 
diff --git a/src/parser.rs b/src/parser.rs
index c8f4e314..3fd6365b 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -25,7 +25,7 @@ use crate::stdlib::{
     borrow::Cow,
     boxed::Box,
     char,
-    collections::HashMap,
+    collections::{HashMap, HashSet},
     fmt, format,
     hash::{Hash, Hasher},
     iter::empty,
@@ -355,7 +355,7 @@ impl fmt::Display for FnAccess {
 /// ## WARNING
 ///
 /// This type is volatile and may change.
-#[derive(Debug, Clone, Hash)]
+#[derive(Debug, Clone)]
 pub struct ScriptFnDef {
     /// Function name.
     pub name: ImmutableString,
@@ -365,7 +365,7 @@ pub struct ScriptFnDef {
     pub params: StaticVec<String>,
     /// Access to external variables.
     #[cfg(not(feature = "no_capture"))]
-    pub externals: StaticVec<String>,
+    pub externals: HashSet<String>,
     /// Function body.
     pub body: Stmt,
     /// Position of the function definition.
diff --git a/src/scope.rs b/src/scope.rs
index 3e43b850..b2024564 100644
--- a/src/scope.rs
+++ b/src/scope.rs
@@ -4,7 +4,9 @@ use crate::any::{Dynamic, Variant};
 use crate::parser::{map_dynamic_to_expr, Expr};
 use crate::token::Position;
 
-use crate::stdlib::{borrow::Cow, boxed::Box, iter, string::String, vec::Vec};
+use crate::stdlib::{
+    borrow::Cow, boxed::Box, collections::HashMap, iter, string::String, vec::Vec,
+};
 
 /// Type of an entry in the Scope.
 #[derive(Debug, Eq, PartialEq, Hash, Copy, Clone)]
@@ -389,13 +391,28 @@ impl<'a> Scope<'a> {
         self
     }
 
+    /// Clone the Scope, keeping only the last instances of each variable name.
+    /// Shadowed variables are omitted in the copy.
+    #[cfg(not(feature = "no_capture"))]
+    pub(crate) fn flatten_clone(&self) -> Self {
+        let mut entries: HashMap<&str, Entry> = Default::default();
+
+        self.0.iter().rev().for_each(|entry| {
+            entries
+                .entry(entry.name.as_ref())
+                .or_insert_with(|| entry.clone());
+        });
+
+        Self(entries.into_iter().map(|(_, v)| v).collect())
+    }
+
     /// Get an iterator to entries in the Scope.
     #[cfg(not(feature = "no_module"))]
     pub(crate) fn into_iter(self) -> impl Iterator<Item = Entry<'a>> {
         self.0.into_iter()
     }
 
-    /// Get an iterator to entries in the Scope.
+    /// Get an iterator to entries in the Scope in reverse order.
     pub(crate) fn to_iter(&self) -> impl Iterator<Item = &Entry> {
         self.0.iter().rev() // Always search a Scope in reverse order
     }