diff --git a/src/cli/README.md b/src/cli/README.md
index 7b308c1ef..d34ae33fd 100644
--- a/src/cli/README.md
+++ b/src/cli/README.md
@@ -20,6 +20,7 @@ OpenThread test scripts use the CLI to execute test cases.
 * [counters](#counters)
 * [dataset](README_DATASET.md)
 * [delaytimermin](#delaytimermin)
+* [diag](#diag)
 * [discover](#discover-channel)
 * [dns](#dns-resolve-hostname-dns-server-ip-dns-server-port)
 * [eidcache](#eidcache)
@@ -65,14 +66,13 @@ OpenThread test scripts use the CLI to execute test cases.
 * [routerselectionjitter](#routerselectionjitter)
 * [routerupgradethreshold](#routerupgradethreshold)
 * [scan](#scan-channel)
+* [service](#service)
 * [singleton](#singleton)
 * [sntp](#sntp-query-sntp-server-ip-sntp-server-port)
 * [state](#state)
 * [thread](#thread-start)
 * [txpower](#txpower)
 * [version](#version)
-* [diag](#diag)
-* [service](#service)
 
 ## OpenThread Command Details
 
diff --git a/src/cli/cli.cpp b/src/cli/cli.cpp
index 4705d41a5..6061209ec 100644
--- a/src/cli/cli.cpp
+++ b/src/cli/cli.cpp
@@ -91,7 +91,6 @@ namespace ot {
 namespace Cli {
 
 const struct Command Interpreter::sCommands[] = {
-    {"help", &Interpreter::ProcessHelp},
     {"bufferinfo", &Interpreter::ProcessBufferInfo},
     {"channel", &Interpreter::ProcessChannel},
 #if OPENTHREAD_FTD
@@ -140,6 +139,7 @@ const struct Command Interpreter::sCommands[] = {
     {"extaddr", &Interpreter::ProcessExtAddress},
     {"extpanid", &Interpreter::ProcessExtPanId},
     {"factoryreset", &Interpreter::ProcessFactoryReset},
+    {"help", &Interpreter::ProcessHelp},
     {"ifconfig", &Interpreter::ProcessIfconfig},
     {"ipaddr", &Interpreter::ProcessIpAddr},
     {"ipmaddr", &Interpreter::ProcessIpMulticastAddr},
diff --git a/src/core/diags/factory_diags.cpp b/src/core/diags/factory_diags.cpp
index 03ba1d7c1..0297c01c6 100644
--- a/src/core/diags/factory_diags.cpp
+++ b/src/core/diags/factory_diags.cpp
@@ -74,8 +74,7 @@ void Diags::ProcessChannel(int aArgCount, char *aArgVector[], char *aOutput, siz
     SuccessOrExit(error = ParseLong(aArgVector[0], value));
     VerifyOrExit(value >= Radio::kChannelMin && value <= Radio::kChannelMax, error = OT_ERROR_INVALID_ARGS);
 
-    mChannel = static_cast<uint8_t>(value);
-    otPlatDiagChannelSet(mChannel);
+    otPlatDiagChannelSet(static_cast<uint8_t>(value));
 
 exit:
     AppendErrorResult(error, aOutput, aOutputMaxLen);
@@ -90,8 +89,7 @@ void Diags::ProcessPower(int aArgCount, char *aArgVector[], char *aOutput, size_
 
     SuccessOrExit(error = ParseLong(aArgVector[0], value));
 
-    mTxPower = static_cast<int8_t>(value);
-    otPlatDiagTxPowerSet(mTxPower);
+    otPlatDiagTxPowerSet(static_cast<int8_t>(value));
 
 exit:
     AppendErrorResult(error, aOutput, aOutputMaxLen);
@@ -132,12 +130,12 @@ const struct Diags::Command Diags::sCommands[] = {
 
 Diags::Diags(Instance &aInstance)
     : InstanceLocator(aInstance)
-    , mTxPower(0)
-    , mChannel(20)
-    , mTxLen(0)
+    , mTxPacket(&Get<Radio>().GetTransmitBuffer())
     , mTxPeriod(0)
     , mTxPackets(0)
-    , mTxPacket(&Get<Radio>().GetTransmitBuffer())
+    , mChannel(20)
+    , mTxPower(0)
+    , mTxLen(0)
     , mRepeatActive(false)
 {
     memset(&mStats, 0, sizeof(mStats));
diff --git a/src/core/diags/factory_diags.hpp b/src/core/diags/factory_diags.hpp
index c3343663b..f10310ce2 100644
--- a/src/core/diags/factory_diags.hpp
+++ b/src/core/diags/factory_diags.hpp
@@ -145,15 +145,18 @@ private:
     static otError ParseLong(char *aString, long &aLong);
 
     static const struct Command sCommands[];
-    struct Stats                mStats;
 
-    int8_t        mTxPower;
-    uint8_t       mChannel;
-    uint8_t       mTxLen;
+#if !OPENTHREAD_RADIO
+    struct Stats mStats;
+
+    otRadioFrame *mTxPacket;
     uint32_t      mTxPeriod;
     uint32_t      mTxPackets;
-    otRadioFrame *mTxPacket;
+    uint8_t       mChannel;
+    int8_t        mTxPower;
+    uint8_t       mTxLen;
     bool          mRepeatActive;
+#endif
 };
 
 #endif // #if OPENTHREAD_CONFIG_DIAG_ENABLE
diff --git a/tests/scripts/thread-cert/test_diag.py b/tests/scripts/thread-cert/test_diag.py
index b72ce25b5..2303952a2 100755
--- a/tests/scripts/thread-cert/test_diag.py
+++ b/tests/scripts/thread-cert/test_diag.py
@@ -51,6 +51,8 @@ class TestDiag(unittest.TestCase):
              'failed\r\nstatus 0xd\r\n'),
             ('diag start\n',
              'start diagnostics mode\r\nstatus 0x00\r\n'),
+            ('diag invalid test\n',
+             'diag feature \'invalid\' is not supported'),
             ('diag',
              'diagnostics mode is enabled\r\n'),
             ('diag channel 10\n',