diff --git a/src/ast.rs b/src/ast.rs
index 9af2bdf2..ca012df1 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -1548,7 +1548,7 @@ pub enum Expr {
     Array(Box<StaticVec<Expr>>, Position),
     /// #{ name:expr, ... }
     Map(
-        Box<(StaticVec<(Ident, Expr)>, BTreeMap<ImmutableString, Dynamic>)>,
+        Box<(StaticVec<(Ident, Expr)>, BTreeMap<Identifier, Dynamic>)>,
         Position,
     ),
     /// ()
diff --git a/src/dynamic.rs b/src/dynamic.rs
index 1ec4d82c..fd730ef3 100644
--- a/src/dynamic.rs
+++ b/src/dynamic.rs
@@ -1712,7 +1712,7 @@ impl<T: Variant + Clone> crate::stdlib::iter::FromIterator<T> for Dynamic {
 }
 #[cfg(not(feature = "no_object"))]
 #[cfg(not(feature = "no_std"))]
-impl<K: Into<ImmutableString>, T: Variant + Clone> From<crate::stdlib::collections::HashMap<K, T>>
+impl<K: Into<crate::Identifier>, T: Variant + Clone> From<crate::stdlib::collections::HashMap<K, T>>
     for Dynamic
 {
     #[inline(always)]
@@ -1729,8 +1729,8 @@ impl<K: Into<ImmutableString>, T: Variant + Clone> From<crate::stdlib::collectio
     }
 }
 #[cfg(not(feature = "no_object"))]
-impl<K: Into<ImmutableString>, T: Variant + Clone> From<crate::stdlib::collections::BTreeMap<K, T>>
-    for Dynamic
+impl<K: Into<crate::Identifier>, T: Variant + Clone>
+    From<crate::stdlib::collections::BTreeMap<K, T>> for Dynamic
 {
     #[inline(always)]
     fn from(value: crate::stdlib::collections::BTreeMap<K, T>) -> Self {
diff --git a/src/engine.rs b/src/engine.rs
index e8255c63..16f32037 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -1573,12 +1573,12 @@ impl Engine {
                     self.make_type_mismatch_err::<ImmutableString>(idx.type_name(), idx_pos)
                 })?;
 
-                if _create && !map.contains_key(index) {
-                    map.insert(index.clone(), Default::default());
+                if _create && !map.contains_key(index.as_str()) {
+                    map.insert(index.clone().into(), Default::default());
                 }
 
                 Ok(map
-                    .get_mut(index)
+                    .get_mut(index.as_str())
                     .map(Target::from)
                     .unwrap_or_else(|| Target::from(())))
             }
diff --git a/src/fn_builtin.rs b/src/fn_builtin.rs
index 3558d098..515c6a68 100644
--- a/src/fn_builtin.rs
+++ b/src/fn_builtin.rs
@@ -85,6 +85,13 @@ pub fn get_builtin_binary_op_fn(
                 Ok(x.$func(y).into())
             })
         };
+        ($xx:ident . $func:ident ( $yy:ident . $yyy:ident () )) => {
+            return Some(|_, args| {
+                let x = &*args[0].read_lock::<$xx>().unwrap();
+                let y = &*args[1].read_lock::<$yy>().unwrap();
+                Ok(x.$func(y.$yyy()).into())
+            })
+        };
         ($func:ident ( $op:tt )) => {
             return Some(|_, args| {
                 let (x, y) = $func(args);
@@ -284,7 +291,7 @@ pub fn get_builtin_binary_op_fn(
         use crate::Map;
 
         match op {
-            OP_CONTAINS => impl_op!(Map.contains_key(ImmutableString)),
+            OP_CONTAINS => impl_op!(Map.contains_key(ImmutableString.as_str())),
             _ => return None,
         }
     }
diff --git a/src/lib.rs b/src/lib.rs
index ae7785ea..146a3717 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -189,7 +189,7 @@ pub type Array = stdlib::vec::Vec<Dynamic>;
 ///
 /// Not available under `no_object`.
 #[cfg(not(feature = "no_object"))]
-pub type Map = stdlib::collections::BTreeMap<ImmutableString, Dynamic>;
+pub type Map = stdlib::collections::BTreeMap<Identifier, Dynamic>;
 
 #[cfg(not(feature = "no_module"))]
 pub use module::ModuleResolver;
diff --git a/src/packages/map_basic.rs b/src/packages/map_basic.rs
index 41212ec0..d76dbcb7 100644
--- a/src/packages/map_basic.rs
+++ b/src/packages/map_basic.rs
@@ -15,7 +15,7 @@ def_package!(crate:BasicMapPackage:"Basic object map utilities.", lib, {
 mod map_functions {
     #[rhai_fn(name = "has", pure)]
     pub fn contains(map: &mut Map, prop: ImmutableString) -> bool {
-        map.contains_key(&prop)
+        map.contains_key(prop.as_str())
     }
     #[rhai_fn(pure)]
     pub fn len(map: &mut Map) -> INT {
@@ -25,7 +25,7 @@ mod map_functions {
         map.clear();
     }
     pub fn remove(map: &mut Map, name: ImmutableString) -> Dynamic {
-        map.remove(&name).unwrap_or_else(|| ().into())
+        map.remove(name.as_str()).unwrap_or_else(|| ().into())
     }
     #[rhai_fn(name = "mixin", name = "+=")]
     pub fn mixin(map: &mut Map, map2: Map) {
diff --git a/src/parser.rs b/src/parser.rs
index 810aba4c..083bd996 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -24,8 +24,8 @@ use crate::syntax::{CustomSyntax, MARKER_BLOCK, MARKER_EXPR, MARKER_IDENT};
 use crate::token::{is_keyword_function, is_valid_identifier, Token, TokenStream};
 use crate::utils::{get_hasher, IdentifierBuilder};
 use crate::{
-    calc_fn_hash, Dynamic, Engine, Identifier, ImmutableString, LexError, ParseError,
-    ParseErrorType, Position, Scope, Shared, StaticVec, AST,
+    calc_fn_hash, Dynamic, Engine, Identifier, LexError, ParseError, ParseErrorType, Position,
+    Scope, Shared, StaticVec, AST,
 };
 
 #[cfg(not(feature = "no_float"))]
@@ -685,7 +685,7 @@ fn parse_map_literal(
     settings.pos = eat_token(input, Token::MapStart);
 
     let mut map: StaticVec<(Ident, Expr)> = Default::default();
-    let mut template: BTreeMap<ImmutableString, Dynamic> = Default::default();
+    let mut template: BTreeMap<Identifier, Dynamic> = Default::default();
 
     loop {
         const MISSING_RBRACE: &str = "to end this object map literal";