diff --git a/dust-lang/src/value.rs b/dust-lang/src/value.rs
index f65c8e8..c2d24e7 100644
--- a/dust-lang/src/value.rs
+++ b/dust-lang/src/value.rs
@@ -82,8 +82,8 @@ impl Value {
         Value::Raw(ValueData::String(to_string.to_string()))
     }
 
-    pub fn list(value: Vec<Value>) -> Self {
-        Value::Raw(ValueData::List(value))
+    pub fn list<T: Into<Vec<Value>>>(values: T) -> Self {
+        Value::Raw(ValueData::List(values.into()))
     }
 
     pub fn map<T: Into<HashMap<Identifier, Value>>>(into_map: T) -> Self {
@@ -737,6 +737,54 @@ impl Display for Value {
     }
 }
 
+impl From<bool> for Value {
+    fn from(value: bool) -> Self {
+        Value::boolean(value)
+    }
+}
+
+impl From<u8> for Value {
+    fn from(value: u8) -> Self {
+        Value::byte(value)
+    }
+}
+
+impl From<char> for Value {
+    fn from(value: char) -> Self {
+        Value::character(value)
+    }
+}
+
+impl From<f64> for Value {
+    fn from(value: f64) -> Self {
+        Value::float(value)
+    }
+}
+
+impl From<i32> for Value {
+    fn from(value: i32) -> Self {
+        Value::integer(value as i64)
+    }
+}
+
+impl From<i64> for Value {
+    fn from(value: i64) -> Self {
+        Value::integer(value)
+    }
+}
+
+impl From<String> for Value {
+    fn from(value: String) -> Self {
+        Value::string(value)
+    }
+}
+
+impl From<&str> for Value {
+    fn from(str: &str) -> Self {
+        Value::string(str)
+    }
+}
+
 impl Eq for Value {}
 
 impl PartialEq for Value {
@@ -1118,54 +1166,6 @@ impl ValueData {
     }
 }
 
-impl From<bool> for ValueData {
-    fn from(value: bool) -> Self {
-        ValueData::Boolean(value)
-    }
-}
-
-impl From<u8> for ValueData {
-    fn from(value: u8) -> Self {
-        ValueData::Byte(value)
-    }
-}
-
-impl From<char> for ValueData {
-    fn from(value: char) -> Self {
-        ValueData::Character(value)
-    }
-}
-
-impl From<f64> for ValueData {
-    fn from(value: f64) -> Self {
-        ValueData::Float(value)
-    }
-}
-
-impl From<i32> for ValueData {
-    fn from(value: i32) -> Self {
-        ValueData::Integer(value as i64)
-    }
-}
-
-impl From<i64> for ValueData {
-    fn from(value: i64) -> Self {
-        ValueData::Integer(value)
-    }
-}
-
-impl From<String> for ValueData {
-    fn from(value: String) -> Self {
-        ValueData::String(value)
-    }
-}
-
-impl From<&str> for ValueData {
-    fn from(value: &str) -> Self {
-        ValueData::String(value.to_string())
-    }
-}
-
 impl Display for ValueData {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         match self {
diff --git a/dust-lang/src/vm.rs b/dust-lang/src/vm.rs
index f06ed2b..74cd42f 100644
--- a/dust-lang/src/vm.rs
+++ b/dust-lang/src/vm.rs
@@ -7,6 +7,7 @@
 use std::{
     collections::HashMap,
     fmt::{self, Display, Formatter},
+    rc::Weak,
     sync::{Arc, Mutex},
 };
 
@@ -242,11 +243,18 @@ impl Vm {
                 let position = value.position();
                 let value = self
                     .run_expression(value, collect_garbage)?
-                    .expect_value(position)?
-                    .into_reference();
+                    .expect_value(position)?;
+
+                let reference = match value {
+                    Value::Raw(_) => value.into_reference(),
+                    Value::Reference(_) => value,
+                    Value::Mutable(_) => {
+                        return Err(RuntimeError::CannotAssignToMutable { position });
+                    }
+                };
 
                 self.context
-                    .set_variable_value(identifier.inner, value)
+                    .set_variable_value(identifier.inner, reference)
                     .map_err(|error| RuntimeError::ContextError { error, position })?;
 
                 Ok(())
@@ -1080,6 +1088,9 @@ impl Vm {
 
 #[derive(Clone, Debug, PartialEq)]
 pub enum RuntimeError {
+    CannotAssignToMutable {
+        position: Span,
+    },
     ConstructError {
         error: ConstructError,
         position: Span,
@@ -1182,6 +1193,7 @@ pub enum RuntimeError {
 impl RuntimeError {
     pub fn position(&self) -> Span {
         match self {
+            Self::CannotAssignToMutable { position } => *position,
             Self::ConstructError { position, .. } => *position,
             Self::ContextError { position, .. } => *position,
             Self::BuiltInFunctionError { position, .. } => *position,
@@ -1233,6 +1245,13 @@ impl From<ParseError> for RuntimeError {
 impl Display for RuntimeError {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         match self {
+            Self::CannotAssignToMutable { position } => {
+                write!(
+                    f,
+                    "Cannot use immutable assignment with a mutable value at {:?}",
+                    position
+                )
+            }
             Self::ConstructError { error, position } => {
                 write!(f, "Constructor error at {:?}: {}", position, error)
             }
@@ -1398,6 +1417,44 @@ mod tests {
 
     use super::*;
 
+    #[test]
+    fn mutate_copied_variable() {
+        let source = "let mut x = 42; let y = [x; 3]; x += 1; y";
+
+        assert_eq!(
+            run(source),
+            Ok(Some(Value::list([43.into(), 43.into(), 43.into()])))
+        );
+    }
+
+    #[test]
+    fn auto_fill_list() {
+        let source = "[42; 3]";
+
+        assert_eq!(
+            run(source),
+            Ok(Some(Value::list(vec![
+                Value::integer(42),
+                Value::integer(42),
+                Value::integer(42)
+            ])))
+        );
+    }
+
+    #[test]
+    fn mutate_assigned_variable() {
+        let source = "let mut x = 42; let mut y = x; x += 1; y";
+
+        assert_eq!(run(source), Ok(Some(Value::integer(43))));
+    }
+
+    #[test]
+    fn assign_to_variable() {
+        let source = "let x = 42; let y = x; y";
+
+        assert_eq!(run(source), Ok(Some(Value::integer(42))));
+    }
+
     #[test]
     fn block_scope_captures_parent() {
         let source = "let x = 42; { x }";