diff --git a/src/posix/platform/netif.cpp b/src/posix/platform/netif.cpp
index a19dd7d77..c53dcf2f4 100644
--- a/src/posix/platform/netif.cpp
+++ b/src/posix/platform/netif.cpp
@@ -464,7 +464,7 @@ static void processMLDEvent(otInstance *aInstance)
     uint8_t             buffer[kMaxMLDEvent];
     ssize_t             bufferLen = -1;
     struct sockaddr_in6 srcAddr;
-    socklen_t           addrLen;
+    socklen_t           addrLen  = sizeof(srcAddr);
     bool                fromSelf = false;
     MLDv2Header *       hdr      = reinterpret_cast<MLDv2Header *>(buffer);
     size_t              offset;