diff --git a/src/core/common/heap_data.cpp b/src/core/common/heap_data.cpp
index 5060fde34..28e1b2f32 100644
--- a/src/core/common/heap_data.cpp
+++ b/src/core/common/heap_data.cpp
@@ -120,10 +120,9 @@ Error Data::UpdateBuffer(uint16_t aNewLength)
 
     VerifyOrExit(aNewLength != mData.GetLength());
 
-    Heap::Free(mData.GetBytes());
-
     if (aNewLength == 0)
     {
+        Heap::Free(mData.GetBytes());
         mData.Init(nullptr, 0);
     }
     else
@@ -131,6 +130,7 @@ Error Data::UpdateBuffer(uint16_t aNewLength)
         uint8_t *newBuffer = static_cast<uint8_t *>(Heap::CAlloc(aNewLength, sizeof(uint8_t)));
 
         VerifyOrExit(newBuffer != nullptr, error = kErrorNoBufs);
+        Heap::Free(mData.GetBytes());
         mData.Init(newBuffer, aNewLength);
     }