diff --git a/src/sdk/main/include/NodeUpdateTransaction.h b/src/sdk/main/include/NodeUpdateTransaction.h
index 36d8fdd2..a7a58686 100644
--- a/src/sdk/main/include/NodeUpdateTransaction.h
+++ b/src/sdk/main/include/NodeUpdateTransaction.h
@@ -274,7 +274,14 @@ class NodeUpdateTransaction : public Transaction<NodeUpdateTransaction>
    * The node identified MUST NOT be deleted.
    * This value is REQUIRED.
    */
-  uint64_t mNodeId;
+  uint64_t mNodeId = 0;
+
+  /**
+   * Flag to track whether nodeId has been explicitly set.
+   * This is necessary because protobuf uint64 defaults to 0, which cannot distinguish
+   * between an explicit 0 and an unset value.
+   */
+  bool mNodeIdSet = false;
 
   /**
    * A Node account identifier.
diff --git a/src/sdk/main/src/NodeUpdateTransaction.cc b/src/sdk/main/src/NodeUpdateTransaction.cc
index 35536494..13003474 100644
--- a/src/sdk/main/src/NodeUpdateTransaction.cc
+++ b/src/sdk/main/src/NodeUpdateTransaction.cc
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: Apache-2.0
 #include "NodeUpdateTransaction.h"
 #include "TransactionId.h"
+#include "exceptions/IllegalStateException.h"
 #include "impl/Node.h"
 #include "impl/Utilities.h"
 
@@ -31,6 +32,7 @@ NodeUpdateTransaction& NodeUpdateTransaction::setNodeId(uint64_t nodeId)
 {
   requireNotFrozen();
   mNodeId = nodeId;
+  mNodeIdSet = true;
   return *this;
 }
 
@@ -148,6 +150,7 @@ void NodeUpdateTransaction::initFromSourceTransactionBody()
   const aproto::NodeUpdateTransactionBody& body = transactionBody.nodeupdate();
 
   mNodeId = body.node_id();
+  mNodeIdSet = true;
   mAccountId = AccountId::fromProtobuf(body.account_id());
 
   if (body.has_description())
@@ -191,6 +194,12 @@ void NodeUpdateTransaction::initFromSourceTransactionBody()
 //-----
 aproto::NodeUpdateTransactionBody* NodeUpdateTransaction::build() const
 {
+  // Validate that nodeId has been explicitly set
+  if (!mNodeIdSet)
+  {
+    throw IllegalStateException("NodeUpdateTransaction requires nodeId to be explicitly set before execution");
+  }
+
   auto body = std::make_unique<aproto::NodeUpdateTransactionBody>();
 
   body->set_node_id(mNodeId);
diff --git a/src/sdk/tests/unit/NodeUpdateTransactionUnitTests.cc b/src/sdk/tests/unit/NodeUpdateTransactionUnitTests.cc
index 56daa66f..0375e199 100644
--- a/src/sdk/tests/unit/NodeUpdateTransactionUnitTests.cc
+++ b/src/sdk/tests/unit/NodeUpdateTransactionUnitTests.cc
@@ -1,6 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0
+#include "AccountId.h"
 #include "ED25519PrivateKey.h"
 #include "NodeUpdateTransaction.h"
+#include "TransactionId.h"
+#include "exceptions/IllegalStateException.h"
 #include "impl/Utilities.h"
 
 #include <gtest/gtest.h>
@@ -226,3 +229,60 @@ TEST_F(NodeUpdateTransactionUnitTests, DeleteGrpcWebProxyEndpoint)
   // Then
   ASSERT_FALSE(transaction.getGrpcWebProxyEndpoint().has_value());
 }
+
+//-----
+TEST_F(NodeUpdateTransactionUnitTests, SetAndGetNodeId)
+{
+  // Given
+  uint64_t nodeId = 5;
+
+  // When
+  transaction.setNodeId(nodeId);
+
+  // Then
+  ASSERT_EQ(transaction.getNodeId(), nodeId);
+}
+
+//-----
+TEST_F(NodeUpdateTransactionUnitTests, ThrowsWhenNodeIdNotSet)
+{
+  // Given
+  NodeUpdateTransaction tx;
+  tx.setTransactionId(TransactionId::generate(AccountId(2)));
+  tx.setNodeAccountIds({ AccountId(3) });
+  tx.setAccountId(AccountId(100));
+  tx.setDescription("Test node");
+
+  // When / Then
+  EXPECT_THROW(tx.freeze(),IllegalStateException);
+}
+
+//-----
+TEST_F(NodeUpdateTransactionUnitTests, SucceedsWhenNodeIdIsSet)
+{
+  // Given
+  NodeUpdateTransaction tx;
+  tx.setTransactionId(TransactionId::generate(AccountId(2)));
+  tx.setNodeAccountIds({ AccountId(3) });
+  tx.setNodeId(5);
+  tx.setAccountId(AccountId(100));
+
+  // When / Then - should not throw
+  EXPECT_NO_THROW(tx.freeze());
+}
+
+//-----
+TEST_F(NodeUpdateTransactionUnitTests, NodeIdSetToZeroIsValid)
+{
+  // Given - nodeId can legitimately be 0 if explicitly set
+  NodeUpdateTransaction tx;
+  tx.setTransactionId(TransactionId::generate(AccountId(2)));
+  tx.setNodeAccountIds({ AccountId(3) });
+  tx.setNodeId(0);
+  tx.setAccountId(AccountId(100));
+
+  // When / Then - should not throw even with nodeId = 0
+  EXPECT_NO_THROW(tx.freeze());
+  EXPECT_EQ(tx.getNodeId(), 0);
+}
+