diff --git a/klippy/extras/tmc.py b/klippy/extras/tmc.py
index 6ed45011..d849c1bb 100644
--- a/klippy/extras/tmc.py
+++ b/klippy/extras/tmc.py
@@ -472,9 +472,11 @@ def TMCMicrostepHelper(config, mcu_tmc):
         and config.get('microsteps', None, note_valid=False) is not None):
         # Older config format with microsteps in tmc config section
         ms_config = config
-    steps = {'256': 0, '128': 1, '64': 2, '32': 3, '16': 4,
-             '8': 5, '4': 6, '2': 7, '1': 8}
-    mres = ms_config.getchoice('microsteps', steps)
+    ms = ms_config.getint('microsteps')
+    mres = {256: 0, 128: 1, 64: 2, 32: 3, 16: 4, 8: 5, 4: 6, 2: 7, 1: 8}.get(ms)
+    if mres is None:
+        raise config.error("Invalid '%s' microstep setting (%d)"
+                           % (config.get_name(), ms))
     fields.set_field("mres", mres)
     fields.set_field("intpol", config.getboolean("interpolate", True))