diff --git a/tests/debug.rs b/tests/debug.rs
index 057c395a03..9aed211af0 100644
--- a/tests/debug.rs
+++ b/tests/debug.rs
@@ -189,3 +189,40 @@ fn source_name() {
     let name = result.lock().unwrap();
     assert_eq!(*name, "test");
 }
+
+
+#[test]
+fn upvars() {
+    let _ = env_logger::init();
+
+    let thread = new_vm();
+    let result = Arc::new(Mutex::new(Vec::new()));
+    {
+        let result = result.clone();
+        let mut context = thread.context();
+        context.set_hook(Some(Box::new(move |_, debug_info| {
+            let stack_info = debug_info.stack_info(0).unwrap();
+            if stack_info.source_name() == "test" {
+                result.lock().unwrap().push(stack_info.upvars().to_owned());
+            }
+            Ok(())
+        })));
+        context.set_hook_mask(CALL_FLAG);
+    }
+    let expr = r#"
+    let x = 1
+    let y = 2
+    let f z =
+        let g w = x
+        g x + y + z
+    f 3
+    "#;
+    Compiler::new()
+        .run_expr::<i32>(&thread, "test", expr)
+        .unwrap();
+
+    assert_eq!(*result.lock().unwrap(),
+               vec![vec![],
+                    vec!["x".to_string(), "+".to_string(), "y".to_string()],
+                    vec!["x".to_string()]]);
+}
diff --git a/vm/src/compiler.rs b/vm/src/compiler.rs
index 36a90bb1d2..2fc072c639 100644
--- a/vm/src/compiler.rs
+++ b/vm/src/compiler.rs
@@ -48,6 +48,7 @@ pub struct CompiledFunction {
     /// Maps instruction indexes to the line that spawned them
     pub source_map: SourceMap,
     pub local_map: LocalMap,
+    pub upvar_names: Vec<String>,
     pub source_name: String,
 }
 
@@ -65,6 +66,7 @@ impl CompiledFunction {
             records: Vec::new(),
             source_map: SourceMap::new(),
             local_map: LocalMap::new(),
+            upvar_names: Vec::new(),
             source_name: source_name,
         }
     }
@@ -120,6 +122,12 @@ impl FunctionEnvs {
         compiler.stack_constructors.exit_scope();
         let instructions = self.function.instructions.len();
         self.function.source_map.close(instructions, current_line);
+        {
+            let function = &mut **self;
+            function.function
+                .upvar_names
+                .extend(function.free_vars.iter().map(|s| s.declared_name().to_string()));
+        }
         self.envs.pop().expect("FunctionEnv in scope")
     }
 }
diff --git a/vm/src/thread.rs b/vm/src/thread.rs
index d64e122f8a..40d81fdb40 100644
--- a/vm/src/thread.rs
+++ b/vm/src/thread.rs
@@ -756,6 +756,13 @@ impl<'a> StackInfo<'a> {
             _ => LocalIter::empty(),
         }
     }
+
+    pub fn upvars(&self) -> &[StdString] {
+        match self.frame().state {
+            State::Closure(ref closure) => &closure.function.upvar_names,
+            _ => panic!("Attempted to access upvar in non closure function"),
+        }
+    }
 }
 
 bitflags! {
diff --git a/vm/src/value.rs b/vm/src/value.rs
index 95a75f511e..fd4ae0e53c 100644
--- a/vm/src/value.rs
+++ b/vm/src/value.rs
@@ -119,6 +119,7 @@ pub struct BytecodeFunction {
     pub records: Vec<Vec<InternedStr>>,
     pub source_map: SourceMap,
     pub local_map: LocalMap,
+    pub upvar_names: Vec<StdString>,
     pub source_name: StdString,
 }
 
diff --git a/vm/src/vm.rs b/vm/src/vm.rs
index b5debd8f02..856e5eef86 100644
--- a/vm/src/vm.rs
+++ b/vm/src/vm.rs
@@ -42,6 +42,7 @@ fn new_bytecode(gc: &mut Gc,
                            records,
                            source_map,
                            local_map,
+                           upvar_names,
                            source_name,
                            .. } = f;
 
@@ -72,6 +73,7 @@ fn new_bytecode(gc: &mut Gc,
         records: records?,
         source_map: source_map,
         local_map: local_map,
+        upvar_names: upvar_names,
         source_name: source_name,
     }))
 }