diff --git a/src/blobstore/implementations/onblocks/impl/DataLeafNode.cpp b/src/blobstore/implementations/onblocks/impl/DataLeafNode.cpp
index 2ec4897d..a26985e2 100644
--- a/src/blobstore/implementations/onblocks/impl/DataLeafNode.cpp
+++ b/src/blobstore/implementations/onblocks/impl/DataLeafNode.cpp
@@ -30,6 +30,11 @@ void DataLeafNode::write(off_t offset, size_t count, const Data &data) {
 void DataLeafNode::InitializeNewNode() {
   *_node.MagicNumber() = _node.magicNumberLeaf;
   *_node.Size() = 0;
+  //fillDataWithZeroes(); not needed, because a newly created block will be zeroed out. DataLeafNodeTest.SpaceIsZeroFilledWhenGrowing ensures this.
+}
+
+void DataLeafNode::fillDataWithZeroesFromTo(off_t begin, off_t end) {
+  std::memset(_node.DataBegin<unsigned char>()+begin, 0, end-begin);
 }
 
 uint64_t DataLeafNode::numBytesInThisNode() {
@@ -39,6 +44,10 @@ uint64_t DataLeafNode::numBytesInThisNode() {
 void DataLeafNode::resize(uint64_t newsize_bytes) {
   assert(newsize_bytes <= MAX_STORED_BYTES);
 
+  if (newsize_bytes < *_node.Size()) {
+    fillDataWithZeroesFromTo(newsize_bytes, *_node.Size());
+  }
+
   *_node.Size() = newsize_bytes;
 }
 
diff --git a/src/blobstore/implementations/onblocks/impl/DataLeafNode.h b/src/blobstore/implementations/onblocks/impl/DataLeafNode.h
index 62034b71..e6991255 100644
--- a/src/blobstore/implementations/onblocks/impl/DataLeafNode.h
+++ b/src/blobstore/implementations/onblocks/impl/DataLeafNode.h
@@ -22,6 +22,8 @@ public:
   uint64_t numBytesInThisNode() override;
   void resize(uint64_t newsize_bytes) override;
 
+private:
+  void fillDataWithZeroesFromTo(off_t begin, off_t end);
 };
 
 }
diff --git a/src/test/blobstore/implementations/onblocks/impl/DataLeafNodeTest.cpp b/src/test/blobstore/implementations/onblocks/impl/DataLeafNodeTest.cpp
index 5d912ce2..4fcc9316 100644
--- a/src/test/blobstore/implementations/onblocks/impl/DataLeafNodeTest.cpp
+++ b/src/test/blobstore/implementations/onblocks/impl/DataLeafNodeTest.cpp
@@ -14,6 +14,7 @@ using std::make_unique;
 using std::string;
 
 using blockstore::BlockStore;
+using blockstore::BlockWithKey;
 using blockstore::Data;
 using blockstore::inmemory::InMemoryBlockStore;
 using namespace blobstore;
@@ -23,9 +24,18 @@ using namespace blobstore::onblocks;
 
 class DataLeafNodeTest: public Test {
 public:
-  unique_ptr<BlockStore> blockStore = make_unique<InMemoryBlockStore>();
 
-  DataLeafNodeTest(): randomData(DataLeafNode::MAX_STORED_BYTES) {
+  DataLeafNodeTest():
+    ZEROES(DataLeafNode::MAX_STORED_BYTES),
+    randomData(DataLeafNode::MAX_STORED_BYTES),
+    blockStore(make_unique<InMemoryBlockStore>()),
+    block(blockStore->create(DataNodeView::BLOCKSIZE_BYTES)),
+    leafblock(blockStore->create(DataNodeView::BLOCKSIZE_BYTES)),
+    leafblockdata((uint8_t*)leafblock.block->data()),
+    leaf(DataNode::createNewLeafNode(std::move(leafblock.block))) {
+
+    ZEROES.FillWithZeroes();
+
     DataBlockFixture dataFixture(DataLeafNode::MAX_STORED_BYTES);
 
     std::memcpy(randomData.data(), dataFixture.data(), randomData.size());
@@ -39,18 +49,27 @@ public:
     return block.key;
   }
 
-  void ReadDataFromLeafBlock(Key key, Data *data) {
+  void FillLeafBlockWithData() {
+    leaf->resize(randomData.size());
+    leaf->write(0, randomData.size(), randomData);
+  }
+
+  void ReadDataFromLoadedLeafBlock(Key key, Data *data) {
     auto leaf = DataNode::load(blockStore->load(key));
     EXPECT_IS_PTR_TYPE(DataLeafNode, leaf.get());
     leaf->read(0, data->size(), data);
   }
 
+  Data ZEROES;
   Data randomData;
+  unique_ptr<BlockStore> blockStore;
+  BlockWithKey block;
+  BlockWithKey leafblock;
+  const uint8_t *leafblockdata;
+  unique_ptr<DataNode> leaf;
 };
 
 TEST_F(DataLeafNodeTest, ReadWrittenDataImmediately) {
-  auto block = blockStore->create(DataNodeView::BLOCKSIZE_BYTES);
-  auto leaf = DataNode::createNewLeafNode(std::move(block.block));
   leaf->resize(randomData.size());
   leaf->write(0, randomData.size(), randomData);
 
@@ -63,19 +82,16 @@ TEST_F(DataLeafNodeTest, ReadWrittenDataAfterReloadingBLock) {
   Key key = WriteDataToNewLeafBlockAndReturnKey();
 
   Data data(DataLeafNode::MAX_STORED_BYTES);
-  ReadDataFromLeafBlock(key, &data);
+  ReadDataFromLoadedLeafBlock(key, &data);
 
   EXPECT_EQ(0, std::memcmp(randomData.data(), data.data(), randomData.size()));
 }
 
 TEST_F(DataLeafNodeTest, NewLeafNodeHasSizeZero) {
-  auto block = blockStore->create(DataNodeView::BLOCKSIZE_BYTES);
-  auto leaf = DataNode::createNewLeafNode(std::move(block.block));
   EXPECT_EQ(0u, leaf->numBytesInThisNode());
 }
 
 TEST_F(DataLeafNodeTest, NewLeafNodeHasSizeZero_AfterLoading) {
-  auto block = blockStore->create(DataNodeView::BLOCKSIZE_BYTES);
   {
     DataNode::createNewLeafNode(std::move(block.block));
   }
@@ -88,14 +104,11 @@ class DataLeafNodeSizeTest: public DataLeafNodeTest, public WithParamInterface<u
 INSTANTIATE_TEST_CASE_P(DataLeafNodeSizeTest, DataLeafNodeSizeTest, Values(0, 1, 5, 16, 32, 512, DataLeafNode::MAX_STORED_BYTES));
 
 TEST_P(DataLeafNodeSizeTest, ResizeNode_ReadSizeImmediately) {
-  auto block = blockStore->create(DataNodeView::BLOCKSIZE_BYTES);
-  auto leaf = DataNode::createNewLeafNode(std::move(block.block));
   leaf->resize(GetParam());
   EXPECT_EQ(GetParam(), leaf->numBytesInThisNode());
 }
 
 TEST_P(DataLeafNodeSizeTest, ResizeNode_ReadSizeAfterLoading) {
-  auto block = blockStore->create(DataNodeView::BLOCKSIZE_BYTES);
   {
     auto leaf = DataNode::createNewLeafNode(std::move(block.block));
     leaf->resize(GetParam());
@@ -104,5 +117,36 @@ TEST_P(DataLeafNodeSizeTest, ResizeNode_ReadSizeAfterLoading) {
   EXPECT_EQ(GetParam(), leaf->numBytesInThisNode());
 }
 
+TEST_F(DataLeafNodeTest, SpaceIsZeroFilledWhenGrowing) {
+  leaf->resize(randomData.size());
+
+  Data read(randomData.size());
+  leaf->read(0, read.size(), &read);
+  EXPECT_EQ(0, std::memcmp(ZEROES.data(), read.data(), read.size()));
+}
+
+TEST_F(DataLeafNodeTest, SpaceGetsZeroFilledWhenShrinkingAndRegrowing) {
+  FillLeafBlockWithData();
+  // resize it smaller and then back to original size
+  uint32_t smaller_size = randomData.size() - 100;
+  leaf->resize(smaller_size);
+  leaf->resize(randomData.size());
+
+  //Check that the space was filled with zeroes
+  Data read(100);
+  leaf->read(smaller_size, read.size(), &read);
+  EXPECT_EQ(0, std::memcmp(ZEROES.data(), read.data(), read.size()));
+}
+
+TEST_F(DataLeafNodeTest, DataGetsZeroFilledWhenShrinking) {
+  FillLeafBlockWithData();
+  uint32_t smaller_size = randomData.size() - 100;
+  //At first, we expect there to be random data in the underlying data block
+  EXPECT_EQ(0, std::memcmp((char*)randomData.data()+smaller_size, leafblockdata+DataNodeView::HEADERSIZE_BYTES+smaller_size, 100));
+
+  //After shrinking, we expect there to be zeroes in the underlying data block
+  leaf->resize(smaller_size);
+  EXPECT_EQ(0, std::memcmp(ZEROES.data(), leafblockdata+DataNodeView::HEADERSIZE_BYTES+smaller_size, 100));
+}
+
 //TODO Write tests that only read part of the data
-//TODO Test numBytesInThisNode()