diff --git a/dom/system/gonk/NetworkUtils.cpp b/dom/system/gonk/NetworkUtils.cpp
index e8bb9ac038b2..c867458e5f34 100644
--- a/dom/system/gonk/NetworkUtils.cpp
+++ b/dom/system/gonk/NetworkUtils.cpp
@@ -819,7 +819,9 @@ void NetworkUtils::postTetherInterfaceList(CommandChain* aChain,
 
   char buf[BUF_SIZE];
   NS_ConvertUTF16toUTF8 reason(aResult.mResultReason);
-  memcpy(buf, reason.get(), reason.Length() + 1);
+
+  size_t length = reason.Length() + 1 < BUF_SIZE ? reason.Length() + 1 : BUF_SIZE;
+  memcpy(buf, reason.get(), length);
   split(buf, INTERFACE_DELIMIT, GET_FIELD(mInterfaceList));
 
   doCommand(command, aChain, aCallback);