diff --git a/docs/Config_Reference.md b/docs/Config_Reference.md
index f0ca2dce2..79f05f121 100644
--- a/docs/Config_Reference.md
+++ b/docs/Config_Reference.md
@@ -5064,15 +5064,16 @@ adc2:
 #   1.50 for cal_dia1 and 2.00 for cal_dia2.
 #raw_dia1: 9500
 #raw_dia2: 10500
-#   The raw calibration values for the sensors. The default is 9500
-#   for raw_dia1 and 10500 for raw_dia2.
+#   The raw calibration values for the sensors. Both values must not be
+#   the same. The default is 9500 for raw_dia1 and 10500 for raw_dia2.
 #default_nominal_filament_diameter: 1.75
 #   The nominal filament diameter. This parameter must be provided.
 #max_difference: 0.200
 #   Maximum allowed filament diameter difference in millimeters (mm).
 #   If difference between nominal filament diameter and sensor output
 #   is more than +- max_difference, extrusion multiplier is set back
-#   to %100. The default is 0.200.
+#   to %100. Must be less than default_nominal_filament_diameter.
+#   The default is 0.200.
 #measurement_delay: 70
 #   The distance from sensor to the melting chamber/hot-end in
 #   millimeters (mm). The filament between the sensor and the hot-end
diff --git a/klippy/extras/hall_filament_width_sensor.py b/klippy/extras/hall_filament_width_sensor.py
index 68180a002..b11b9d94e 100644
--- a/klippy/extras/hall_filament_width_sensor.py
+++ b/klippy/extras/hall_filament_width_sensor.py
@@ -35,6 +35,14 @@ class HallFilamentWidthSensor:
         self.is_log =config.getboolean('logging', False)
         self.enable_flow_compensation = config.getboolean(
             'enable_flow_compensation', True)
+        if self.rawdia1 == self.rawdia2:
+            raise config.error(
+                "hall_filament_width_sensor: raw_dia1 and raw_dia2 must be"
+                " different")
+        if self.min_diameter <= 0:
+            raise config.error(
+                "hall_filament_width_sensor: max_difference must be less than"
+                " default_nominal_filament_diameter")
         # Use the current diameter instead of nominal while the first
         # measurement isn't in place
         self.use_current_dia_while_delay = config.getboolean(