diff --git a/src/core/coap/coap_message.cpp b/src/core/coap/coap_message.cpp
index c8c336668..edf4584b6 100644
--- a/src/core/coap/coap_message.cpp
+++ b/src/core/coap/coap_message.cpp
@@ -45,7 +45,7 @@ namespace Coap {
 
 void Message::Init(void)
 {
-    memset(&GetHelpData(), 0, sizeof(GetHelpData()));
+    GetHelpData().Clear();
     SetVersion(kVersion1);
     SetOffset(0);
     GetHelpData().mHeaderLength = kMinHeaderLength;
@@ -211,7 +211,7 @@ const otCoapOption *Message::GetFirstOption(void)
 {
     const otCoapOption *option = NULL;
 
-    memset(&GetHelpData().mOption, 0, sizeof(GetHelpData().mOption));
+    GetHelpData().ClearOption();
 
     VerifyOrExit(GetLength() - GetHelpData().mHeaderOffset >= GetOptionStart());
 
@@ -346,7 +346,7 @@ otError Message::ParseHeader(void)
            sizeof(GetHelpData()) +
                static_cast<size_t>((reinterpret_cast<uint8_t *>(&GetHelpData()) - mBuffer.mHead.mData)));
 
-    memset(&GetHelpData(), 0, sizeof(GetHelpData()));
+    GetHelpData().Clear();
 
     GetHelpData().mHeaderOffset = GetOffset();
     Read(GetHelpData().mHeaderOffset, sizeof(GetHelpData().mHeader), &GetHelpData().mHeader);
diff --git a/src/core/coap/coap_message.hpp b/src/core/coap/coap_message.hpp
index 5f110dfe9..de13f5062 100644
--- a/src/core/coap/coap_message.hpp
+++ b/src/core/coap/coap_message.hpp
@@ -585,6 +585,9 @@ private:
      */
     struct HelpData
     {
+        void Clear(void) { memset(this, 0, sizeof(*this)); }
+        void ClearOption(void) { memset(&mOption, 0, sizeof(mOption)); }
+
         Header       mHeader;
         otCoapOption mOption;
         uint16_t     mNextOptionOffset; ///< The byte offset for the next CoAP Option