diff --git a/crates/engine/src/lisp/drawing.rs b/crates/engine/src/lisp/drawing.rs
index 7e85dd67..b4076fce 100644
--- a/crates/engine/src/lisp/drawing.rs
+++ b/crates/engine/src/lisp/drawing.rs
@@ -1069,7 +1069,14 @@ pub fn distof(_ctx: &mut Ctx<'_>, a: Vec<Value>) -> Result<Flow, LispError> {
 pub fn angtof(ctx: &mut Ctx<'_>, a: Vec<Value>) -> Result<Flow, LispError> {
     arity(&a, 1, 2)?;
     let s = string(&a[0])?;
-    Ok(Flow::Value(ctx.s.angle_settings().direction(&s).map(Value::Real).unwrap_or_default()))
+    let mut settings = ctx.s.angle_settings();
+    // AUNITS 0..=4; any other units argument is an error in AutoCAD, nil here.
+    match a.get(1) {
+        None | Some(Value::Nil) => {}
+        Some(Value::Int(u)) if (0..=4).contains(u) => settings.aunits = i64::from(*u),
+        Some(_) => return Ok(Flow::Value(Value::Nil)),
+    }
+    Ok(Flow::Value(settings.direction(&s).map(Value::Real).unwrap_or_default()))
 }
 
 /// `(trans pt from to [disp])`: points are in the world system throughout (no UCS yet).
diff --git a/crates/engine/src/lisp/tests.rs b/crates/engine/src/lisp/tests.rs
index b3a09e79..bee6d7d3 100644
--- a/crates/engine/src/lisp/tests.rs
+++ b/crates/engine/src/lisp/tests.rs
@@ -782,3 +782,12 @@ fn a_panic_inside_a_routine_ends_it_with_an_error() {
     assert!(s.log.iter().any(|l| l.contains("internal error")), "{:?}", s.log);
     assert_eq!(ok(&mut s, "(+ 1 2)"), "3");
 }
+
+#[test]
+fn angtof_reads_the_string_in_the_given_units() {
+    let mut s = Session::new();
+    assert_eq!(ok(&mut s, "(angtof \"1.5\" 3)"), "1.5");
+    assert_eq!(ok(&mut s, "(angtof \"180\" 0)"), "3.14159");
+    assert_eq!(ok(&mut s, "(angtof \"180\" 7)"), "nil");
+    assert_eq!(ok(&mut s, "(angtof \"180\" \"x\")"), "nil");
+}