diff --git a/tests/query_device.py b/tests/query_device.py
index ba272f0..51d07af 100755
--- a/tests/query_device.py
+++ b/tests/query_device.py
@@ -122,6 +122,7 @@ for name, number in all_registers.items():
 if action == 'read' or action == 'all':
     print('---- Register readout ----')
     for register in register_name + register_number:
+        signed = False
         if isinstance(register, str):
             reg_name = register
             if reg_name in all_registers:
@@ -134,7 +135,9 @@ if action == 'read' or action == 'all':
             # try reverse lookup
             reg_name = all_register_numbers[reg_number] if reg_number in all_register_numbers else ''
         try:
-            result = int(s.read_register(reg_number))
+            signed = '_signed' in reg_name
+            print(f'DEBUG: register {reg_name} is {signed} (signed)')
+            result = int(s.read_register(reg_number, signed=signed))
         except:
             result = 'N/A'
         print(f'{reg_number : <10} {result : <10} {reg_name}')
diff --git a/tests/sensor.py b/tests/sensor.py
index 227d7ba..92a2a1a 100644
--- a/tests/sensor.py
+++ b/tests/sensor.py
@@ -112,7 +112,7 @@ class Sensor:
     def RH_SCD4x(self):
         return self.read_register(self.input_registers['RH_SCD4x'])
 
-    def read_register(self, register_number, retries=10):
+    def read_register(self, register_number, signed=False, retries=10):
         if self.input_register_start <= register_number <= self.input_register_end:
             function_code = 4
             register_offset = register_number - self.input_register_start
@@ -127,7 +127,7 @@ class Sensor:
             try:
                 self.readout_total += 1
                 # minimalmodbus divides received register value by 10
-                return self.serial.read_register(register_offset, 1, functioncode=function_code) * 10
+                return self.serial.read_register(register_offset, 1, functioncode=function_code, signed=signed) * 10
             except minimalmodbus.NoResponseError as e:
                 last_exception = e
                 self.readout_error_no_response += 1