@@ -61,6 +61,15 @@ impl PackError {
         };
         Self { kind, exception }
     }
+
+    /// An error that is the answer exactly as it was raised. `pack_single()`
+    /// leaves `'?'` to `PyObject_IsTrue()` this way, with no message of its own.
+    fn raised(exception: PyBaseExceptionRef) -> Self {
+        Self {
+            kind: PackErrorKind::Raised,
+            exception,
+        }
+    }
 }
 
 static OVERFLOW_MSG: &str = "total struct size too long"; // not a const to reduce code size
@@ -803,7 +812,7 @@ impl Packable for bool {
         data: &mut [u8],
     ) -> Result<(), PackError> {
         let v = ArgIntoBool::try_from_object(vm, arg)
-            .map_err(|e| PackError::from_exception(e, vm))?
+            .map_err(PackError::raised)?
             .into_bool() as u8;
         v.pack_int::<E>(data);
         Ok(())
 
@@ -764,3 +764,25 @@ def test_delete_answers_readonly_first():
 test_setitem_error_kinds()
 test_setitem_propagates_index_errors()
 test_delete_answers_readonly_first()
+
+
+def test_bool_format_keeps_its_own_error():
+    # Deciding truth is the value's own code, and what it raises is the answer.
+    class Raises:
+        def __init__(self, exc):
+            self.exc = exc
+
+        def __bool__(self):
+            raise self.exc
+
+    view = memoryview(bytearray(b"\x00")).cast("?")
+    for exc in (ZeroDivisionError("boom"), ValueError("nope"), TypeError("nah")):
+        try:
+            view[0] = Raises(exc)
+        except type(exc) as e:
+            assert str(e) == str(exc), e
+        else:
+            raise AssertionError(f"expected {type(exc).__name__}")
+
+
+test_bool_format_keeps_its_own_error()