diff --git a/src/modbus.c b/src/modbus.c
index 994f9b3..74ce28c 100644
--- a/src/modbus.c
+++ b/src/modbus.c
@@ -212,7 +212,12 @@ int zbx_modbus_read_registers(AGENT_REQUEST *request, AGENT_RESULT *result)
 		modbus_free(ctx);
 		return SYSINFO_RET_FAIL;
 	}
-	modbus_set_slave(ctx, slave_id);
+	if (modbus_set_slave(ctx, slave_id) == -1)
+	{
+		SET_MSG_RESULT(result, strdup("Check slaveid parameter"));
+		modbus_free(ctx);
+		return SYSINFO_RET_FAIL;
+	}
 
 	//<reg> set register to start from
 	errno = 0;
diff --git a/tests/test_01modbus_errors.py b/tests/test_01modbus_errors.py
index 4d1df75..a0508ec 100644
--- a/tests/test_01modbus_errors.py
+++ b/tests/test_01modbus_errors.py
@@ -63,7 +63,7 @@ def test_bad_register_string(self, host):
 
     def test_bad_slaveid_integer(self, host):
         key = "modbus_read_registers["+host+",5000,99,3,uint32,BE,0]"
-        assert zabbix_get(key) == 'ZBX_NOTSUPPORTED: Illegal data address'
+        assert zabbix_get(key) == 'ZBX_NOTSUPPORTED: Check slaveid parameter'
     def test_bad_slaveid_string(self, host):
         key = "modbus_read_registers["+host+",bad,1,3,uint32,BE,0]"
-        assert zabbix_get(key) == 'ZBX_NOTSUPPORTED: Check slaveid parameter'        
+        assert zabbix_get(key) == 'ZBX_NOTSUPPORTED: Check slaveid parameter'