diff --git a/src/any.rs b/src/any.rs
index 4a330cff..5182da08 100644
--- a/src/any.rs
+++ b/src/any.rs
@@ -18,7 +18,6 @@ use crate::stdlib::{
     boxed::Box,
     collections::HashMap,
     fmt,
-    hash::Hash,
     string::String,
     vec::Vec,
 };
diff --git a/src/engine.rs b/src/engine.rs
index 16205a2f..0a5ec70a 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -710,7 +710,7 @@ impl Engine {
         /// This function restores the first argument that was replaced by `normalize_first_arg_of_method_call`.
         fn restore_first_arg<'a>(old_this_ptr: Option<&'a mut Dynamic>, args: &mut FnCallArgs<'a>) {
             if let Some(this_pointer) = old_this_ptr {
-                mem::replace(args.get_mut(0).unwrap(), this_pointer);
+                args[0] = this_pointer;
             }
         }
 
diff --git a/src/module.rs b/src/module.rs
index 3ee25995..7216c248 100644
--- a/src/module.rs
+++ b/src/module.rs
@@ -30,6 +30,7 @@ use crate::stdlib::{
 };
 
 #[cfg(not(feature = "no_std"))]
+#[cfg(feature = "sync")]
 use crate::stdlib::sync::RwLock;
 
 /// Return type of module-level Rust function.
diff --git a/src/packages/arithmetic.rs b/src/packages/arithmetic.rs
index 8aeb1590..5e43c05b 100644
--- a/src/packages/arithmetic.rs
+++ b/src/packages/arithmetic.rs
@@ -8,6 +8,7 @@ use crate::token::Position;
 use crate::parser::FLOAT;
 
 #[cfg(not(feature = "no_float"))]
+#[cfg(feature = "no_std")]
 use num_traits::*;
 
 use num_traits::{
diff --git a/src/packages/math_basic.rs b/src/packages/math_basic.rs
index ca0bc374..aed7e5b7 100644
--- a/src/packages/math_basic.rs
+++ b/src/packages/math_basic.rs
@@ -7,6 +7,7 @@ use crate::token::Position;
 use crate::parser::FLOAT;
 
 #[cfg(not(feature = "no_float"))]
+#[cfg(feature = "no_std")]
 use num_traits::*;
 
 use crate::stdlib::{boxed::Box, format, i32, i64};
diff --git a/tests/call_fn.rs b/tests/call_fn.rs
index a04bd614..97767df7 100644
--- a/tests/call_fn.rs
+++ b/tests/call_fn.rs
@@ -1,7 +1,6 @@
 #![cfg(not(feature = "no_function"))]
 use rhai::{
-    Dynamic, Engine, EvalAltResult, FnPtr, Func, ImmutableString, Module, ParseError,
-    ParseErrorType, Scope, INT,
+    Dynamic, Engine, EvalAltResult, FnPtr, Func, Module, ParseError, ParseErrorType, Scope, INT,
 };
 
 #[test]