diff --git a/oden-js/src/lib.rs b/oden-js/src/lib.rs
index e4171675..cf11d155 100644
--- a/oden-js/src/lib.rs
+++ b/oden-js/src/lib.rs
@@ -16,7 +16,7 @@ pub use atom::{Atom, AtomRef};
 pub use class::{Class, ClassID};
 pub use context::{Context, ContextRef, EvalFlags};
 pub use conversion::*;
-pub use promise::Promise;
+pub use promise::{DefaultRejectedPromiseTracker, Promise, RejectedPromiseTracker};
 pub use runtime::Runtime;
 pub use value::{Value, ValueRef, ValueType};
 
diff --git a/oden-js/src/promise.rs b/oden-js/src/promise.rs
index 8ee23b26..03cabee8 100644
--- a/oden-js/src/promise.rs
+++ b/oden-js/src/promise.rs
@@ -1,4 +1,4 @@
-use crate::{ContextRef, ValueResult};
+use crate::{ContextRef, ValueRef, ValueResult};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::mpsc::Sender;
 
@@ -72,3 +72,53 @@ impl Drop for Promise {
         assert!(self.complete);
     }
 }
+
+pub trait RejectedPromiseTracker {
+    fn on_rejected_promise(
+        &self,
+        ctx: &ContextRef,
+        promise: &ValueRef,
+        reason: &ValueRef,
+        is_handled: bool,
+    );
+}
+
+impl<T> RejectedPromiseTracker for T
+where
+    T: Fn(&ContextRef, &ValueRef, &ValueRef, bool) -> (),
+{
+    fn on_rejected_promise(
+        &self,
+        ctx: &ContextRef,
+        promise: &ValueRef,
+        reason: &ValueRef,
+        is_handled: bool,
+    ) {
+        self(ctx, promise, reason, is_handled);
+    }
+}
+
+pub struct DefaultRejectedPromiseTracker {}
+
+impl DefaultRejectedPromiseTracker {
+    pub fn new() -> Self {
+        DefaultRejectedPromiseTracker {}
+    }
+}
+
+impl RejectedPromiseTracker for DefaultRejectedPromiseTracker {
+    fn on_rejected_promise(
+        &self,
+        ctx: &ContextRef,
+        _promise: &ValueRef,
+        reason: &ValueRef,
+        is_handled: bool,
+    ) {
+        if !is_handled {
+            let reason_str = reason.to_string(ctx).expect(
+                "Unhandled rejected promise: reason unknown: unable to convert reason to string",
+            );
+            panic!("Unhandled rejected promise: {reason_str}");
+        }
+    }
+}
diff --git a/oden-js/src/runtime.rs b/oden-js/src/runtime.rs
index e349d955..5c1fb4ab 100644
--- a/oden-js/src/runtime.rs
+++ b/oden-js/src/runtime.rs
@@ -1,7 +1,8 @@
 use crate::{
     module::loader::{load_module, DefaultModuleLoader, ModuleLoader},
     promise::{PromiseEvent, PromiseHandle},
-    ContextRef, Promise, Result, Value,
+    ContextRef, DefaultRejectedPromiseTracker, Promise, RejectedPromiseTracker, Result, Value,
+    ValueRef,
 };
 use oden_js_sys as sys;
 use std::cell::{RefCell, RefMut};
@@ -45,20 +46,19 @@ struct PrivateState {
     promise_send: Sender<(PromiseHandle, PromiseEvent)>,
     promise_recv: Receiver<(PromiseHandle, PromiseEvent)>,
     promise_table: HashMap<PromiseHandle, PromiseEntry>, // !
+    rejection_tracker: Arc<Box<dyn RejectedPromiseTracker>>,
 }
 
 impl PrivateState {
-    pub fn new<T>(loader: T) -> Box<RefCell<Self>>
-    where
-        T: ModuleLoader + 'static,
-    {
+    pub fn new() -> Box<RefCell<Self>> {
         let (send, recv) = channel();
         Box::new(RefCell::new(PrivateState {
             refs: 1,
-            loader: Arc::new(Box::new(loader)),
+            loader: Arc::new(Box::new(DefaultModuleLoader::new())),
             promise_send: send,
             promise_recv: recv,
             promise_table: HashMap::new(),
+            rejection_tracker: Arc::new(Box::new(DefaultRejectedPromiseTracker::new())),
         }))
     }
 
@@ -92,6 +92,28 @@ impl PrivateState {
         let context = ContextRef::from_raw(ctx);
         load_module(&context, path, &loader)
     }
+
+    unsafe extern "C" fn promise_rejection_tracker(
+        ctx: *mut sys::JSContext,
+        promise: sys::JSValue,
+        reason: sys::JSValue,
+        is_handled: i32,
+        opaque: *mut std::os::raw::c_void,
+    ) {
+        let ctx = ContextRef::from_raw(ctx);
+        let promise = ValueRef::from_raw(promise);
+        let reason = ValueRef::from_raw(reason);
+        let is_handled = is_handled != 0;
+        let handler = unsafe {
+            let ptr = opaque as *const RefCell<PrivateState>;
+            ptr.as_ref()
+                .expect("We already know this runtime is one of ours!")
+                .borrow()
+                .rejection_tracker
+                .clone()
+        };
+        handler.on_rejected_promise(&ctx, &promise, &reason, is_handled);
+    }
 }
 
 #[derive(Debug)]
@@ -101,16 +123,17 @@ pub struct Runtime {
 
 impl Runtime {
     pub fn new() -> Runtime {
-        Self::with_loader(DefaultModuleLoader::new())
-    }
-
-    pub fn with_loader<TLoader: ModuleLoader + 'static>(loader: TLoader) -> Runtime {
-        let state = PrivateState::new(loader);
+        let state = PrivateState::new();
         let rt = unsafe {
             let rt = sys::JS_NewRuntime();
             let state = Box::into_raw(state) as *mut _;
             sys::JS_SetRuntimeOpaque(rt, state);
             sys::JS_SetModuleLoaderFunc(rt, None, Some(PrivateState::module_loader), state);
+            sys::JS_SetHostPromiseRejectionTracker(
+                rt,
+                Some(PrivateState::promise_rejection_tracker),
+                state,
+            );
             rt
         };
         Runtime { rt }
@@ -141,6 +164,26 @@ impl Runtime {
         }
     }
 
+    /// Set the handler for loading modules. By default this is an instance
+    /// of `DefaultModuleLoader`.
+    pub fn set_module_loader<T>(&mut self, loader: T)
+    where
+        T: ModuleLoader + 'static,
+    {
+        let mut state = unsafe { PrivateState::from_rt_mut(self.rt) };
+        state.loader = Arc::new(Box::new(loader));
+    }
+
+    /// Set a tracker to be notified whenever a promise is rejected. By
+    /// default, this is an instance of `DefaultRejectedPromiseHandler`.
+    pub fn set_rejected_promise_tracker<T>(&mut self, tracker: T)
+    where
+        T: RejectedPromiseTracker + 'static,
+    {
+        let mut state = unsafe { PrivateState::from_rt_mut(self.rt) };
+        state.rejection_tracker = Arc::new(Box::new(tracker));
+    }
+
     pub fn run_gc(&mut self) {
         unsafe {
             sys::JS_RunGC(self.rt);
diff --git a/src/script.rs b/src/script.rs
index 4d38a705..5d9b0c2e 100644
--- a/src/script.rs
+++ b/src/script.rs
@@ -56,7 +56,8 @@ pub struct ScriptContext {
 
 impl ScriptContext {
     pub fn new() -> Self {
-        let runtime = Runtime::with_loader(Loader::new());
+        let mut runtime = Runtime::new();
+        runtime.set_module_loader(Loader::new());
 
         let mut context = Context::new(runtime);
         context.add_intrinsic_bigfloat();