diff --git a/examples/drivers/windows/otLwf/radio.c b/examples/drivers/windows/otLwf/radio.c
index 709e383fd..8fb575d44 100644
--- a/examples/drivers/windows/otLwf/radio.c
+++ b/examples/drivers/windows/otLwf/radio.c
@@ -476,12 +476,14 @@ otLwfRadioReceiveFrame(
     LogFuncExit(DRIVER_DATA_PATH);
 }
 
-ThreadError otPlatRadioTransmit(_In_ otInstance *otCtx)
+ThreadError otPlatRadioTransmit(_In_ otInstance *otCtx, _In_ RadioPacket *aPacket)
 {
     NT_ASSERT(otCtx);
     PMS_FILTER pFilter = otCtxToFilter(otCtx);
     ThreadError error = kThreadError_Busy;
-    
+
+    UNREFERENCED_PARAMETER(aPacket);
+
     LogFuncEntryMsg(DRIVER_DATA_PATH, "Filter: %p", pFilter);
 
     NT_ASSERT(pFilter->otPhyState == kStateReceive);
@@ -576,19 +578,19 @@ otLwfRadioTransmitFrameDone(
         POT_NBL_CONTEXT SendNblContext = GetNBLContext(pFilter->SendNetBufferList);
         BOOLEAN FramePending = (SendNblContext->Flags & OT_NBL_FLAG_ACK_FRAME_PENDING) != 0 || pFilter->CountPendingRecvNBLs != 0;
 
-        otPlatRadioTransmitDone(pFilter->otCtx, FramePending, kThreadError_None);
+        otPlatRadioTransmitDone(pFilter->otCtx, &pFilter->otTransmitFrame, FramePending, kThreadError_None);
     }
     else if (STATUS_DEVICE_BUSY == pFilter->SendNetBufferList->Status)
     {
-        otPlatRadioTransmitDone(pFilter->otCtx, false, kThreadError_ChannelAccessFailure);
+        otPlatRadioTransmitDone(pFilter->otCtx, &pFilter->otTransmitFrame, false, kThreadError_ChannelAccessFailure);
     }
     else if (STATUS_TIMEOUT == pFilter->SendNetBufferList->Status)
     {
-        otPlatRadioTransmitDone(pFilter->otCtx, false, kThreadError_NoAck);
+        otPlatRadioTransmitDone(pFilter->otCtx, &pFilter->otTransmitFrame, false, kThreadError_NoAck);
     }
     else
     {
-        otPlatRadioTransmitDone(pFilter->otCtx, false, kThreadError_Abort);
+        otPlatRadioTransmitDone(pFilter->otCtx, &pFilter->otTransmitFrame, false, kThreadError_Abort);
     }
 
     LogFuncExit(DRIVER_DATA_PATH);
diff --git a/examples/platforms/cc2538/radio.c b/examples/platforms/cc2538/radio.c
index ee2c8ebbd..bec34e8d4 100644
--- a/examples/platforms/cc2538/radio.c
+++ b/examples/platforms/cc2538/radio.c
@@ -251,7 +251,7 @@ ThreadError otPlatRadioReceive(otInstance *aInstance, uint8_t aChannel)
     return error;
 }
 
-ThreadError otPlatRadioTransmit(otInstance *aInstance)
+ThreadError otPlatRadioTransmit(otInstance *aInstance, RadioPacket *aPacket)
 {
     ThreadError error = kThreadError_InvalidState;
     (void)aInstance;
@@ -271,15 +271,15 @@ ThreadError otPlatRadioTransmit(otInstance *aInstance)
         HWREG(RFCORE_SFR_RFST) = RFCORE_SFR_RFST_INSTR_FLUSHTX;
 
         // frame length
-        HWREG(RFCORE_SFR_RFDATA) = sTransmitFrame.mLength;
+        HWREG(RFCORE_SFR_RFDATA) = aPacket->mLength;
 
         // frame data
-        for (i = 0; i < sTransmitFrame.mLength; i++)
+        for (i = 0; i < aPacket->mLength; i++)
         {
-            HWREG(RFCORE_SFR_RFDATA) = sTransmitFrame.mPsdu[i];
+            HWREG(RFCORE_SFR_RFDATA) = aPacket->mPsdu[i];
         }
 
-        setChannel(sTransmitFrame.mChannel);
+        setChannel(aPacket->mChannel);
 
         while ((HWREG(RFCORE_XREG_FSMSTAT1) & 1) == 0);
 
@@ -406,12 +406,12 @@ void cc2538RadioProcess(otInstance *aInstance)
 
             if (otPlatDiagModeGet())
             {
-                otPlatDiagRadioTransmitDone(aInstance, false, sTransmitError);
+                otPlatDiagRadioTransmitDone(aInstance, &sTransmitFrame, false, sTransmitError);
             }
             else
 #endif
             {
-                otPlatRadioTransmitDone(aInstance, false, sTransmitError);
+                otPlatRadioTransmitDone(aInstance, &sTransmitFrame, false, sTransmitError);
             }
         }
         else if (sReceiveFrame.mLength == IEEE802154_ACK_LENGTH &&
@@ -424,12 +424,14 @@ void cc2538RadioProcess(otInstance *aInstance)
 
             if (otPlatDiagModeGet())
             {
-                otPlatDiagRadioTransmitDone(aInstance, (sReceiveFrame.mPsdu[0] & IEEE802154_FRAME_PENDING) != 0, sTransmitError);
+                otPlatDiagRadioTransmitDone(aInstance, &sTransmitFrame, (sReceiveFrame.mPsdu[0] & IEEE802154_FRAME_PENDING) != 0,
+                                            sTransmitError);
             }
             else
 #endif
             {
-                otPlatRadioTransmitDone(aInstance, (sReceiveFrame.mPsdu[0] & IEEE802154_FRAME_PENDING) != 0, sTransmitError);
+                otPlatRadioTransmitDone(aInstance, &sTransmitFrame, (sReceiveFrame.mPsdu[0] & IEEE802154_FRAME_PENDING) != 0,
+                                        sTransmitError);
             }
         }
     }
diff --git a/examples/platforms/posix/radio.c b/examples/platforms/posix/radio.c
index 8007e6a3d..9d082dd11 100644
--- a/examples/platforms/posix/radio.c
+++ b/examples/platforms/posix/radio.c
@@ -427,10 +427,11 @@ ThreadError otPlatRadioReceive(otInstance *aInstance, uint8_t aChannel)
     return error;
 }
 
-ThreadError otPlatRadioTransmit(otInstance *aInstance)
+ThreadError otPlatRadioTransmit(otInstance *aInstance, RadioPacket *aPacket)
 {
     ThreadError error = kThreadError_InvalidState;
     (void)aInstance;
+    (void)aPacket;
 
     if (sState == kStateReceive)
     {
@@ -489,12 +490,12 @@ void radioReceive(otInstance *aInstance)
 
         if (otPlatDiagModeGet())
         {
-            otPlatDiagRadioTransmitDone(aInstance, isFramePending(sReceiveFrame.mPsdu), kThreadError_None);
+            otPlatDiagRadioTransmitDone(aInstance, &sTransmitFrame, isFramePending(sReceiveFrame.mPsdu), kThreadError_None);
         }
         else
 #endif
         {
-            otPlatRadioTransmitDone(aInstance, isFramePending(sReceiveFrame.mPsdu), kThreadError_None);
+            otPlatRadioTransmitDone(aInstance, &sTransmitFrame, isFramePending(sReceiveFrame.mPsdu), kThreadError_None);
         }
     }
     else if ((sState == kStateReceive || sState == kStateTransmit) &&
@@ -520,12 +521,12 @@ void radioSendMessage(otInstance *aInstance)
 
         if (otPlatDiagModeGet())
         {
-            otPlatDiagRadioTransmitDone(aInstance, false, kThreadError_None);
+            otPlatDiagRadioTransmitDone(aInstance, &sTransmitFrame, false, kThreadError_None);
         }
         else
 #endif
         {
-            otPlatRadioTransmitDone(aInstance, false, kThreadError_None);
+            otPlatRadioTransmitDone(aInstance, &sTransmitFrame, false, kThreadError_None);
         }
     }
 }
diff --git a/include/platform/radio.h b/include/platform/radio.h
index 70ec3152a..50c215b7a 100644
--- a/include/platform/radio.h
+++ b/include/platform/radio.h
@@ -354,16 +354,18 @@ RadioPacket *otPlatRadioGetTransmitBuffer(otInstance *aInstance);
  * 2. Transmits the psdu on the given channel and at the given transmit power.
  *
  * @param[in] aInstance  The OpenThread instance structure.
+ * @param[in] aPacket    A pointer to the packet that will be transmitted.
  *
  * @retval ::kThreadError_None         Successfully transitioned to Transmit.
  * @retval ::kThreadError_InvalidState The radio was not in the Receive state.
  */
-ThreadError otPlatRadioTransmit(otInstance *aInstance);
+ThreadError otPlatRadioTransmit(otInstance *aInstance, RadioPacket *aPacket);
 
 /**
  * The radio driver calls this method to notify OpenThread that the transmission has completed.
  *
  * @param[in]  aInstance      The OpenThread instance structure.
+ * @param[in]  aPacket        A pointer to the packet that was transmitted.
  * @param[in]  aFramePending  TRUE if an ACK frame was received and the Frame Pending bit was set.
  * @param[in]  aError  ::kThreadError_None when the frame was transmitted, ::kThreadError_NoAck when the frame was
  *                     transmitted but no ACK was received, ::kThreadError_ChannelAccessFailure when the transmission
@@ -371,7 +373,8 @@ ThreadError otPlatRadioTransmit(otInstance *aInstance);
  *                     aborted for other reasons.
  *
  */
-extern void otPlatRadioTransmitDone(otInstance *aInstance, bool aFramePending, ThreadError aError);
+extern void otPlatRadioTransmitDone(otInstance *aInstance, RadioPacket *aPacket, bool aFramePending,
+                                    ThreadError aError);
 
 /**
  * Get the most recent RSSI measurement.
@@ -413,6 +416,7 @@ void otPlatRadioSetPromiscuous(otInstance *aInstance, bool aEnable);
  * The radio driver calls this method to notify OpenThread diagnostics module that the transmission has completed.
  *
  * @param[in]  aInstance      The OpenThread instance structure.
+ * @param[in]  aPacket        A pointer to the packet that was transmitted.
  * @param[in]  aFramePending  TRUE if an ACK frame was received and the Frame Pending bit was set.
  * @param[in]  aError  ::kThreadError_None when the frame was transmitted, ::kThreadError_NoAck when the frame was
  *                     transmitted but no ACK was received, ::kThreadError_ChannelAccessFailure when the transmission
@@ -420,7 +424,8 @@ void otPlatRadioSetPromiscuous(otInstance *aInstance, bool aEnable);
  *                     aborted for other reasons.
  *
  */
-extern void otPlatDiagRadioTransmitDone(otInstance *aInstance, bool aFramePending, ThreadError aError);
+extern void otPlatDiagRadioTransmitDone(otInstance *aInstance, RadioPacket *aPacket, bool aFramePending,
+                                        ThreadError aError);
 
 /**
  * The radio driver calls this method to notify OpenThread diagnostics module of a received packet.
diff --git a/src/core/mac/mac.cpp b/src/core/mac/mac.cpp
index d32b02900..5d494f173 100644
--- a/src/core/mac/mac.cpp
+++ b/src/core/mac/mac.cpp
@@ -162,6 +162,7 @@ Mac::Mac(ThreadNetif &aThreadNetif):
     mPcapCallbackContext = NULL;
 
     otPlatRadioEnable(mNetif.GetInstance());
+    mTxFrame = static_cast<Frame *>(otPlatRadioGetTransmitBuffer(mNetif.GetInstance()));
 }
 
 ThreadError Mac::ActiveScan(uint32_t aScanChannels, uint16_t aScanDuration, ActiveScanHandler aHandler, void *aContext)
@@ -288,6 +289,7 @@ void Mac::EnergyScanDone(int8_t aEnergyScanMaxRssi)
         // and start the next transmission task
         if (mScanChannels == 0 || mScanChannel > kPhyMaxChannel)
         {
+            otPlatRadioReceive(mNetif.GetInstance(), mChannel);
             mEnergyScanHandler(mScanContext, NULL);
             ScheduleNextTransmission();
             ExitNow();
@@ -717,7 +719,7 @@ exit:
 
 void Mac::HandleBeginTransmit(void)
 {
-    Frame &sendFrame(*static_cast<Frame *>(otPlatRadioGetTransmitBuffer(mNetif.GetInstance())));
+    Frame &sendFrame(*mTxFrame);
     ThreadError error = kThreadError_None;
 
     if (mCsmaAttempts == 0 && mTransmitAttempts == 0)
@@ -761,7 +763,7 @@ void Mac::HandleBeginTransmit(void)
 
     error = otPlatRadioReceive(mNetif.GetInstance(), sendFrame.GetChannel());
     assert(error == kThreadError_None);
-    error = otPlatRadioTransmit(mNetif.GetInstance());
+    error = otPlatRadioTransmit(mNetif.GetInstance(), static_cast<RadioPacket *>(&sendFrame));
     assert(error == kThreadError_None);
 
     if (sendFrame.GetAckRequest() && !(otPlatRadioGetCaps(mNetif.GetInstance()) & kRadioCapsAckTimeout))
@@ -784,9 +786,11 @@ exit:
     }
 }
 
-extern "C" void otPlatRadioTransmitDone(otInstance *aInstance, bool aRxPending, ThreadError aError)
+extern "C" void otPlatRadioTransmitDone(otInstance *aInstance, RadioPacket *aPacket, bool aRxPending,
+                                        ThreadError aError)
 {
     otLogFuncEntryMsg("%!otError!, aRxPending=%u", aError, aRxPending ? 1 : 0);
+    (void)aPacket;
     aInstance->mThreadNetif.GetMac().TransmitDoneTask(aRxPending, aError);
     otLogFuncExit();
 }
@@ -842,8 +846,6 @@ void Mac::HandleMacTimer(void *aContext)
 
 void Mac::HandleMacTimer(void)
 {
-    otPlatRadioReceive(mNetif.GetInstance(), mChannel);
-
     switch (mState)
     {
     case kStateActiveScan:
@@ -854,6 +856,7 @@ void Mac::HandleMacTimer(void)
 
             if (mScanChannels == 0 || mScanChannel > kPhyMaxChannel)
             {
+                otPlatRadioReceive(mNetif.GetInstance(), mChannel);
                 otPlatRadioSetPanId(mNetif.GetInstance(), mPanId);
                 mActiveScanHandler(mScanContext, NULL);
                 ScheduleNextTransmission();
@@ -871,6 +874,7 @@ void Mac::HandleMacTimer(void)
 
     case kStateTransmitData:
         otLogDebgMac("ack timer fired");
+        otPlatRadioReceive(mNetif.GetInstance(), mChannel);
         mCounters.mTxTotal++;
         SentFrame(kThreadError_NoAck);
         break;
@@ -901,7 +905,7 @@ void Mac::HandleReceiveTimer(void)
 
 void Mac::SentFrame(ThreadError aError)
 {
-    Frame &sendFrame(*static_cast<Frame *>(otPlatRadioGetTransmitBuffer(mNetif.GetInstance())));
+    Frame &sendFrame(*mTxFrame);
     Sender *sender;
 
     switch (aError)
diff --git a/src/core/mac/mac.hpp b/src/core/mac/mac.hpp
index 89fe143e4..389b6a6ff 100644
--- a/src/core/mac/mac.hpp
+++ b/src/core/mac/mac.hpp
@@ -648,6 +648,8 @@ private:
     Whitelist mWhitelist;
     Blacklist mBlacklist;
 
+    Frame *mTxFrame;
+
     otMacCounters mCounters;
 };
 
diff --git a/src/diag/diag_process.cpp b/src/diag/diag_process.cpp
index c049bcc22..44e04a6bc 100644
--- a/src/diag/diag_process.cpp
+++ b/src/diag/diag_process.cpp
@@ -61,6 +61,8 @@ uint8_t Diag::sChannel;
 uint8_t Diag::sTxLen;
 uint32_t Diag::sTxPeriod;
 uint32_t Diag::sTxPackets;
+RadioPacket * Diag::sTxPacket;
+
 otInstance *Diag::sContext;
 
 void Diag::Init(otInstance *aInstance)
@@ -72,6 +74,7 @@ void Diag::Init(otInstance *aInstance)
     sTxLen = 0;
     sTxPackets = 0;
     memset(&sStats, 0, sizeof(struct DiagStats));
+    sTxPacket = otPlatRadioGetTransmitBuffer(sContext);
 }
 
 char *Diag::ProcessCmd(int argc, char *argv[])
@@ -174,23 +177,21 @@ ThreadError Diag::ParseLong(char *argv, long &value)
 
 void Diag::TxPacket()
 {
-    RadioPacket *packet = otPlatRadioGetTransmitBuffer(sContext);
-
     if (sTxPackets > 0)
     {
         sTxPackets--;
     }
 
-    packet->mLength = sTxLen;
-    packet->mChannel = sChannel;
-    packet->mPower = sTxPower;
+    sTxPacket->mLength = sTxLen;
+    sTxPacket->mChannel = sChannel;
+    sTxPacket->mPower = sTxPower;
 
     for (uint8_t i = 0; i < sTxLen; i++)
     {
-        packet->mPsdu[i] = i;
+        sTxPacket->mPsdu[i] = i;
     }
 
-    otPlatRadioTransmit(sContext);
+    otPlatRadioTransmit(sContext, sTxPacket);
 }
 
 void Diag::ProcessChannel(int argc, char *argv[], char *aOutput, size_t aOutputMaxLen)
@@ -375,8 +376,10 @@ extern "C" void otPlatDiagAlarmFired(otInstance *aInstance)
     Diag::AlarmFired(aInstance);
 }
 
-extern "C" void otPlatDiagRadioTransmitDone(otInstance *aInstance, bool aRxPending, ThreadError aError)
+extern "C" void otPlatDiagRadioTransmitDone(otInstance *aInstance, RadioPacket *aPacket, bool aRxPending, ThreadError aError)
 {
+    (void)aPacket;
+
     Diag::DiagTransmitDone(aInstance, aRxPending, aError);
 }
 
diff --git a/src/diag/diag_process.hpp b/src/diag/diag_process.hpp
index e13084ebf..bacaf294e 100644
--- a/src/diag/diag_process.hpp
+++ b/src/diag/diag_process.hpp
@@ -92,6 +92,7 @@ private:
     static uint8_t sTxLen;
     static uint32_t sTxPeriod;
     static uint32_t sTxPackets;
+    static RadioPacket *sTxPacket;
     static otInstance *sContext;
 };
 
diff --git a/tests/unit/test_diag.cpp b/tests/unit/test_diag.cpp
index 269ab6409..fcb0123ea 100644
--- a/tests/unit/test_diag.cpp
+++ b/tests/unit/test_diag.cpp
@@ -55,8 +55,9 @@ extern "C" void otPlatAlarmFired(otInstance *)
 {
 }
 
-extern "C" void otPlatRadioTransmitDone(otInstance *, bool aRxPending, ThreadError aError)
+extern "C" void otPlatRadioTransmitDone(otInstance *, RadioPacket *aFrame, bool aRxPending, ThreadError aError)
 {
+    (void)aFrame;
     (void)aRxPending;
     (void)aError;
 }
diff --git a/tests/unit/test_fuzz.cpp b/tests/unit/test_fuzz.cpp
index 5d6598d4f..589e5d4f4 100644
--- a/tests/unit/test_fuzz.cpp
+++ b/tests/unit/test_fuzz.cpp
@@ -145,7 +145,7 @@ void TestFuzz(uint32_t aSeconds)
             if (g_fTransmit)
             {
                 g_fTransmit = false;
-                otPlatRadioTransmitDone(aInstance, true, kThreadError_None);
+                otPlatRadioTransmitDone(aInstance, &g_TransmitRadioPacket, true, kThreadError_None);
 #ifdef DBG_FUZZ
                 Log("<== transmit");
 #endif
diff --git a/tests/unit/test_platform.cpp b/tests/unit/test_platform.cpp
index a9f1508c6..7517ce984 100644
--- a/tests/unit/test_platform.cpp
+++ b/tests/unit/test_platform.cpp
@@ -203,8 +203,10 @@ extern "C" {
         }
     }
 
-    ThreadError otPlatRadioTransmit(otInstance *aInstance)
+    ThreadError otPlatRadioTransmit(otInstance *aInstance, RadioPacket *aPacket)
     {
+        (void)aPacket;
+
         if (g_testPlatRadioTransmit)
         {
             return g_testPlatRadioTransmit(aInstance);
@@ -346,7 +348,7 @@ exit:
     {
     }
 
-    void otPlatDiagRadioTransmitDone(otInstance *, bool, ThreadError)
+    void otPlatDiagRadioTransmitDone(otInstance *, RadioPacket *, bool, ThreadError)
     {
     }