diff --git a/src/module.rs b/src/module.rs
index 4d70b169..51d5539c 100644
--- a/src/module.rs
+++ b/src/module.rs
@@ -4,10 +4,11 @@ use crate::any::{Dynamic, Variant};
 use crate::calc_fn_hash;
 use crate::engine::Engine;
 use crate::fn_native::{CallableFunction as Func, FnCallArgs, IteratorFn, SendSync};
+use crate::fn_register::by_value as cast_arg;
 use crate::parser::{FnAccess, FnAccess::Public, ScriptFnDef};
 use crate::result::EvalAltResult;
 use crate::token::{Position, Token};
-use crate::utils::{StaticVec, StraightHasherBuilder};
+use crate::utils::{ImmutableString, StaticVec, StraightHasherBuilder};
 
 #[cfg(not(feature = "no_function"))]
 use crate::fn_native::Shared;
@@ -32,7 +33,6 @@ use crate::stdlib::{
     collections::HashMap,
     fmt, format,
     iter::empty,
-    mem,
     num::NonZeroUsize,
     ops::{Deref, DerefMut},
     string::{String, ToString},
@@ -396,9 +396,21 @@ impl Module {
             arg_types.len()
         };
 
-        let hash_fn = calc_fn_hash(empty(), &name, args_len, arg_types.iter().cloned());
+        let params = arg_types
+            .into_iter()
+            .cloned()
+            .map(|id| {
+                if id == TypeId::of::<&str>() {
+                    TypeId::of::<ImmutableString>()
+                } else if id == TypeId::of::<String>() {
+                    TypeId::of::<ImmutableString>()
+                } else {
+                    id
+                }
+            })
+            .collect();
 
-        let params = arg_types.into_iter().cloned().collect();
+        let hash_fn = calc_fn_hash(empty(), &name, args_len, arg_types.iter().cloned());
 
         self.functions
             .insert(hash_fn, (name, access, params, func.into()));
@@ -518,7 +530,7 @@ impl Module {
         func: impl Fn(A) -> FuncReturn<T> + SendSync + 'static,
     ) -> u64 {
         let f = move |_: &Engine, _: &Module, args: &mut FnCallArgs| {
-            func(mem::take(args[0]).cast::<A>()).map(Dynamic::from)
+            func(cast_arg::<A>(&mut args[0])).map(Dynamic::from)
         };
         let arg_types = [TypeId::of::<A>()];
         self.set_fn(name, Public, &arg_types, Func::from_pure(Box::new(f)))
@@ -592,8 +604,8 @@ impl Module {
         func: impl Fn(A, B) -> FuncReturn<T> + SendSync + 'static,
     ) -> u64 {
         let f = move |_: &Engine, _: &Module, args: &mut FnCallArgs| {
-            let a = mem::take(args[0]).cast::<A>();
-            let b = mem::take(args[1]).cast::<B>();
+            let a = cast_arg::<A>(&mut args[0]);
+            let b = cast_arg::<B>(&mut args[1]);
 
             func(a, b).map(Dynamic::from)
         };
@@ -623,7 +635,7 @@ impl Module {
         func: impl Fn(&mut A, B) -> FuncReturn<T> + SendSync + 'static,
     ) -> u64 {
         let f = move |_: &Engine, _: &Module, args: &mut FnCallArgs| {
-            let b = mem::take(args[1]).cast::<B>();
+            let b = cast_arg::<B>(&mut args[1]);
             let a = &mut args[0].write_lock::<A>().unwrap();
 
             func(a, b).map(Dynamic::from)
@@ -709,9 +721,9 @@ impl Module {
         func: impl Fn(A, B, C) -> FuncReturn<T> + SendSync + 'static,
     ) -> u64 {
         let f = move |_: &Engine, _: &Module, args: &mut FnCallArgs| {
-            let a = mem::take(args[0]).cast::<A>();
-            let b = mem::take(args[1]).cast::<B>();
-            let c = mem::take(args[2]).cast::<C>();
+            let a = cast_arg::<A>(&mut args[0]);
+            let b = cast_arg::<B>(&mut args[1]);
+            let c = cast_arg::<C>(&mut args[2]);
 
             func(a, b, c).map(Dynamic::from)
         };
@@ -746,8 +758,8 @@ impl Module {
         func: impl Fn(&mut A, B, C) -> FuncReturn<T> + SendSync + 'static,
     ) -> u64 {
         let f = move |_: &Engine, _: &Module, args: &mut FnCallArgs| {
-            let b = mem::take(args[1]).cast::<B>();
-            let c = mem::take(args[2]).cast::<C>();
+            let b = cast_arg::<B>(&mut args[2]);
+            let c = cast_arg::<C>(&mut args[3]);
             let a = &mut args[0].write_lock::<A>().unwrap();
 
             func(a, b, c).map(Dynamic::from)
@@ -780,8 +792,8 @@ impl Module {
         func: impl Fn(&mut A, B, C) -> FuncReturn<()> + SendSync + 'static,
     ) -> u64 {
         let f = move |_: &Engine, _: &Module, args: &mut FnCallArgs| {
-            let b = mem::take(args[1]).cast::<B>();
-            let c = mem::take(args[2]).cast::<C>();
+            let b = cast_arg::<B>(&mut args[1]);
+            let c = cast_arg::<C>(&mut args[2]);
             let a = &mut args[0].write_lock::<A>().unwrap();
 
             func(a, b, c).map(Dynamic::from)
@@ -858,10 +870,10 @@ impl Module {
         func: impl Fn(A, B, C, D) -> FuncReturn<T> + SendSync + 'static,
     ) -> u64 {
         let f = move |_: &Engine, _: &Module, args: &mut FnCallArgs| {
-            let a = mem::take(args[0]).cast::<A>();
-            let b = mem::take(args[1]).cast::<B>();
-            let c = mem::take(args[2]).cast::<C>();
-            let d = mem::take(args[3]).cast::<D>();
+            let a = cast_arg::<A>(&mut args[0]);
+            let b = cast_arg::<B>(&mut args[1]);
+            let c = cast_arg::<C>(&mut args[2]);
+            let d = cast_arg::<D>(&mut args[3]);
 
             func(a, b, c, d).map(Dynamic::from)
         };
@@ -902,9 +914,9 @@ impl Module {
         func: impl Fn(&mut A, B, C, D) -> FuncReturn<T> + SendSync + 'static,
     ) -> u64 {
         let f = move |_: &Engine, _: &Module, args: &mut FnCallArgs| {
-            let b = mem::take(args[1]).cast::<B>();
-            let c = mem::take(args[2]).cast::<C>();
-            let d = mem::take(args[3]).cast::<D>();
+            let b = cast_arg::<B>(&mut args[1]);
+            let c = cast_arg::<C>(&mut args[2]);
+            let d = cast_arg::<D>(&mut args[3]);
             let a = &mut args[0].write_lock::<A>().unwrap();
 
             func(a, b, c, d).map(Dynamic::from)
diff --git a/tests/modules.rs b/tests/modules.rs
index 0744fd8c..e3475584 100644
--- a/tests/modules.rs
+++ b/tests/modules.rs
@@ -1,7 +1,7 @@
 #![cfg(not(feature = "no_module"))]
 use rhai::{
-    module_resolvers::StaticModuleResolver, Dynamic, Engine, EvalAltResult, Module, ParseError,
-    ParseErrorType, Scope, INT,
+    module_resolvers::StaticModuleResolver, Dynamic, Engine, EvalAltResult, ImmutableString,
+    Module, ParseError, ParseErrorType, Scope, INT,
 };
 
 #[test]
@@ -79,12 +79,12 @@ fn test_module_resolver() -> Result<(), Box<EvalAltResult>> {
     });
 
     #[cfg(not(feature = "no_float"))]
-        module.set_fn_4_mut(
+    module.set_fn_4_mut(
         "sum_of_three_args".to_string(),
         |target: &mut INT, a: INT, b: INT, c: f64| {
             *target = a + b + c as INT;
             Ok(())
-        }
+        },
     );
 
     resolver.insert("hello", module);
@@ -316,3 +316,41 @@ fn test_module_export() -> Result<(), Box<EvalAltResult>> {
 
     Ok(())
 }
+
+#[test]
+fn test_module_str() -> Result<(), Box<EvalAltResult>> {
+    fn test_fn(_input: ImmutableString) -> Result<INT, Box<EvalAltResult>> {
+        Ok(42)
+    }
+    fn test_fn2(_input: &str) -> Result<INT, Box<EvalAltResult>> {
+        Ok(42)
+    }
+    fn test_fn3(_input: String) -> Result<INT, Box<EvalAltResult>> {
+        Ok(42)
+    }
+
+    let mut engine = rhai::Engine::new();
+    let mut module = Module::new();
+    module.set_fn_1("test", test_fn);
+    module.set_fn_1("test2", test_fn2);
+    module.set_fn_1("test3", test_fn3);
+
+    let mut static_modules = rhai::module_resolvers::StaticModuleResolver::new();
+    static_modules.insert("test", module);
+    engine.set_module_resolver(Some(static_modules));
+
+    assert_eq!(
+        engine.eval::<INT>(r#"import "test" as test; test::test("test");"#)?,
+        42
+    );
+    assert_eq!(
+        engine.eval::<INT>(r#"import "test" as test; test::test2("test");"#)?,
+        42
+    );
+    assert_eq!(
+        engine.eval::<INT>(r#"import "test" as test; test::test3("test");"#)?,
+        42
+    );
+
+    Ok(())
+}