diff --git a/thin-provisioning/superblock_validator.cc b/thin-provisioning/superblock_validator.cc
index 3369054..2d59d65 100644
--- a/thin-provisioning/superblock_validator.cc
+++ b/thin-provisioning/superblock_validator.cc
@@ -11,7 +11,7 @@ namespace {
         unsigned const SECTOR_TO_BLOCK_SHIFT = 3;
 	uint32_t const SUPERBLOCK_CSUM_SEED = 160774;
 
-	struct validator : public block_manager<>::validator {
+	struct sb_validator : public block_manager<>::validator {
 		virtual void check(buffer<> const &b, block_address location) const {
 			superblock_disk const *sbd = reinterpret_cast<superblock_disk const *>(&b);
 			crc32c sum(SUPERBLOCK_CSUM_SEED);
@@ -34,7 +34,7 @@ namespace {
 block_manager<>::validator::ptr
 thin_provisioning::superblock_validator()
 {
-	return block_manager<>::validator::ptr(new validator);
+	return block_manager<>::validator::ptr(new sb_validator);
 }
 
 //----------------------------------------------------------------
diff --git a/unit-tests/Makefile.in b/unit-tests/Makefile.in
index 0e8bfa7..101efc8 100644
--- a/unit-tests/Makefile.in
+++ b/unit-tests/Makefile.in
@@ -40,6 +40,7 @@ lib/libgmock.a: $(GMOCK_DEPS)
 
 TEST_SOURCE=\
 	unit-tests/gmock_main.cc \
+	unit-tests/test_utils.cc \
 	\
 	unit-tests/array_block_t.cc \
 	unit-tests/array_t.cc \
diff --git a/unit-tests/metadata_checker_t.cc b/unit-tests/metadata_checker_t.cc
index 36e5c2c..d2a169c 100644
--- a/unit-tests/metadata_checker_t.cc
+++ b/unit-tests/metadata_checker_t.cc
@@ -120,8 +120,7 @@ namespace {
 		}
 
 		void corrupt_superblock() {
-			block_manager<>::write_ref wr = bm_->write_lock(0);
-			wr.data()[57] = 0;
+			zero_block(bm_, SUPERBLOCK_LOCATION);
 		}
 
 		with_temp_directory dir_;
diff --git a/unit-tests/test_utils.cc b/unit-tests/test_utils.cc
new file mode 100644
index 0000000..9e82df1
--- /dev/null
+++ b/unit-tests/test_utils.cc
@@ -0,0 +1,11 @@
+#include "test_utils.h"
+
+//----------------------------------------------------------------
+
+void test::zero_block(block_manager<>::ptr bm, block_address b)
+{
+	block_manager<>::write_ref wr = bm->write_lock(b);
+	memset(&wr.data(), 0, sizeof(wr.data()));
+}
+
+//----------------------------------------------------------------
diff --git a/unit-tests/test_utils.h b/unit-tests/test_utils.h
index 8d68b65..a773e09 100644
--- a/unit-tests/test_utils.h
+++ b/unit-tests/test_utils.h
@@ -35,6 +35,8 @@ namespace test {
 			new block_manager<BlockSize>(path, nr, MAX_HELD_LOCKS,
 						     block_io<BlockSize>::CREATE));
 	}
+
+	void zero_block(block_manager<>::ptr bm, block_address b);
 }
 
 //----------------------------------------------------------------