diff --git a/core/src/avm2/globals/boolean.rs b/core/src/avm2/globals/boolean.rs
index 9c1217813..073edc881 100644
--- a/core/src/avm2/globals/boolean.rs
+++ b/core/src/avm2/globals/boolean.rs
@@ -4,18 +4,31 @@ use crate::avm2::activation::Activation;
 use crate::avm2::class::Class;
 use crate::avm2::method::Method;
 use crate::avm2::names::{Namespace, QName};
-use crate::avm2::object::{primitive_allocator, Object};
+use crate::avm2::object::{primitive_allocator, Object, TObject};
 use crate::avm2::value::Value;
 use crate::avm2::Error;
 use gc_arena::{GcCell, MutationContext};
 
 /// Implements `Boolean`'s instance initializer.
 pub fn instance_init<'gc>(
-    _activation: &mut Activation<'_, 'gc, '_>,
-    _this: Option<Object<'gc>>,
-    _args: &[Value<'gc>],
+    activation: &mut Activation<'_, 'gc, '_>,
+    this: Option<Object<'gc>>,
+    args: &[Value<'gc>],
 ) -> Result<Value<'gc>, Error> {
-    Err("Boolean constructor is a stub.".into())
+    if let Some(this) = this {
+        if let Some(mut prim) = this.as_primitive_mut(activation.context.gc_context) {
+            if matches!(*prim, Value::Undefined | Value::Null) {
+                *prim = args
+                    .get(0)
+                    .cloned()
+                    .unwrap_or(Value::Bool(false))
+                    .coerce_to_boolean()
+                    .into();
+            }
+        }
+    }
+
+    Ok(Value::Undefined)
 }
 
 /// Implements `Boolean`'s native instance initializer.
diff --git a/core/src/avm2/globals/number.rs b/core/src/avm2/globals/number.rs
index 08688ac9e..a35569300 100644
--- a/core/src/avm2/globals/number.rs
+++ b/core/src/avm2/globals/number.rs
@@ -11,11 +11,24 @@ use gc_arena::{GcCell, MutationContext};
 
 /// Implements `Number`'s instance initializer.
 pub fn instance_init<'gc>(
-    _activation: &mut Activation<'_, 'gc, '_>,
-    _this: Option<Object<'gc>>,
-    _args: &[Value<'gc>],
+    activation: &mut Activation<'_, 'gc, '_>,
+    this: Option<Object<'gc>>,
+    args: &[Value<'gc>],
 ) -> Result<Value<'gc>, Error> {
-    Err("Number constructor is a stub.".into())
+    if let Some(this) = this {
+        if let Some(mut prim) = this.as_primitive_mut(activation.context.gc_context) {
+            if matches!(*prim, Value::Undefined | Value::Null) {
+                *prim = args
+                    .get(0)
+                    .cloned()
+                    .unwrap_or(Value::Number(0.0))
+                    .coerce_to_number(activation)?
+                    .into();
+            }
+        }
+    }
+
+    Ok(Value::Undefined)
 }
 
 /// Implements `Number`'s native instance initializer.
diff --git a/core/src/avm2/globals/uint.rs b/core/src/avm2/globals/uint.rs
index e67cb8a89..4d45d4ce5 100644
--- a/core/src/avm2/globals/uint.rs
+++ b/core/src/avm2/globals/uint.rs
@@ -4,18 +4,31 @@ use crate::avm2::activation::Activation;
 use crate::avm2::class::Class;
 use crate::avm2::method::{Method, ParamConfig};
 use crate::avm2::names::{Namespace, QName};
-use crate::avm2::object::{primitive_allocator, Object};
+use crate::avm2::object::{primitive_allocator, Object, TObject};
 use crate::avm2::value::Value;
 use crate::avm2::Error;
 use gc_arena::{GcCell, MutationContext};
 
 /// Implements `uint`'s instance initializer.
 pub fn instance_init<'gc>(
-    _activation: &mut Activation<'_, 'gc, '_>,
-    _this: Option<Object<'gc>>,
-    _args: &[Value<'gc>],
+    activation: &mut Activation<'_, 'gc, '_>,
+    this: Option<Object<'gc>>,
+    args: &[Value<'gc>],
 ) -> Result<Value<'gc>, Error> {
-    Err("uint constructor is a stub.".into())
+    if let Some(this) = this {
+        if let Some(mut prim) = this.as_primitive_mut(activation.context.gc_context) {
+            if matches!(*prim, Value::Undefined | Value::Null) {
+                *prim = args
+                    .get(0)
+                    .cloned()
+                    .unwrap_or(Value::Undefined)
+                    .coerce_to_u32(activation)?
+                    .into();
+            }
+        }
+    }
+
+    Ok(Value::Undefined)
 }
 
 /// Implements `uint`'s native instance initializer.
@@ -45,16 +58,7 @@ pub fn create_class<'gc>(mc: MutationContext<'gc, '_>) -> GcCell<'gc, Class<'gc>
     let class = Class::new(
         QName::new(Namespace::public(), "uint"),
         Some(QName::new(Namespace::public(), "Object").into()),
-        Method::from_builtin_and_params(
-            instance_init,
-            "<uint instance initializer>",
-            vec![ParamConfig::of_type(
-                "num",
-                QName::new(Namespace::public(), "Object").into(),
-            )],
-            false,
-            mc,
-        ),
+        Method::from_builtin(instance_init, "<uint instance initializer>", mc),
         Method::from_builtin(class_init, "<uint class initializer>", mc),
         mc,
     );