diff --git a/include/openthread/instance.h b/include/openthread/instance.h
index bf7dfb60c..65c6df56b 100644
--- a/include/openthread/instance.h
+++ b/include/openthread/instance.h
@@ -53,7 +53,7 @@ extern "C" {
  * @note This number versions both OpenThread platform and user APIs.
  *
  */
-#define OPENTHREAD_API_VERSION (127)
+#define OPENTHREAD_API_VERSION (128)
 
 /**
  * @addtogroup api-instance
diff --git a/include/openthread/platform/radio.h b/include/openthread/platform/radio.h
index bba9d7699..8fd87d463 100644
--- a/include/openthread/platform/radio.h
+++ b/include/openthread/platform/radio.h
@@ -68,6 +68,7 @@ extern "C" {
 enum
 {
     OT_RADIO_FRAME_MAX_SIZE    = 127,    ///< aMaxPHYPacketSize (IEEE 802.15.4-2006)
+    OT_RADIO_FRAME_MIN_SIZE    = 3,      ///< Minimal size of frame FCS + CONTROL
     OT_RADIO_SYMBOLS_PER_OCTET = 2,      ///< 2.4 GHz IEEE 802.15.4-2006
     OT_RADIO_BIT_RATE          = 250000, ///< 2.4 GHz IEEE 802.15.4 (bits per second)
     OT_RADIO_BITS_PER_OCTET    = 8,      ///< Number of bits per octet
diff --git a/src/core/diags/README.md b/src/core/diags/README.md
index 2dc027918..ba2a9ec75 100644
--- a/src/core/diags/README.md
+++ b/src/core/diags/README.md
@@ -77,6 +77,8 @@ status 0x00
 
 Transmit a fixed number of packets with fixed length.
 
+Length parameter has to be in range [3, 127].
+
 ```bash
 > diag send 20 100
 sending 0x14 packet(s), length 0x64
@@ -87,6 +89,8 @@ status 0x00
 
 Transmit packets repeatedly with a fixed interval.
 
+Length parameter has to be in range [3, 127].
+
 ```bash
 > diag repeat 100 100
 sending packets of length 0x64 at the delay of 0x64 ms
diff --git a/src/core/diags/factory_diags.cpp b/src/core/diags/factory_diags.cpp
index 73de633b1..6b6d109f5 100644
--- a/src/core/diags/factory_diags.cpp
+++ b/src/core/diags/factory_diags.cpp
@@ -244,6 +244,7 @@ Error Diags::ProcessRepeat(uint8_t aArgsLength, char *aArgs[], char *aOutput, si
 
         SuccessOrExit(error = ParseLong(aArgs[1], value));
         VerifyOrExit(value <= OT_RADIO_FRAME_MAX_SIZE, error = kErrorInvalidArgs);
+        VerifyOrExit(value >= OT_RADIO_FRAME_MIN_SIZE, error = kErrorInvalidArgs);
         mTxLen = static_cast<uint8_t>(value);
 
         mRepeatActive = true;
@@ -271,6 +272,7 @@ Error Diags::ProcessSend(uint8_t aArgsLength, char *aArgs[], char *aOutput, size
 
     SuccessOrExit(error = ParseLong(aArgs[1], value));
     VerifyOrExit(value <= OT_RADIO_FRAME_MAX_SIZE, error = kErrorInvalidArgs);
+    VerifyOrExit(value >= OT_RADIO_FRAME_MIN_SIZE, error = kErrorInvalidArgs);
     mTxLen = static_cast<uint8_t>(value);
 
     snprintf(aOutput, aOutputMaxLen, "sending %#x packet(s), length %#x\r\nstatus 0x%02x\r\n",