diff --git a/test-tool/test_writesame10_0blocks.c b/test-tool/test_writesame10_0blocks.c
index cc07488..4bcd001 100644
--- a/test-tool/test_writesame10_0blocks.c
+++ b/test-tool/test_writesame10_0blocks.c
@@ -40,6 +40,7 @@ test_writesame10_0blocks(void)
 	logging(LOG_VERBOSE, LOG_BLANK_LINE);
 	logging(LOG_VERBOSE, "Test WRITESAME10 0-blocks at LBA==0 (WSNZ=%d)",
 		inq_bl->wsnz);
+	memset(buf, 0, block_size);
 	ret = writesame10(sd, 0,
 			  block_size, 0, 0, 0, 0, 0, buf,
 			  EXPECT_STATUS_GOOD);
diff --git a/test-tool/test_writesame16_0blocks.c b/test-tool/test_writesame16_0blocks.c
index 68cff38..b9091c4 100644
--- a/test-tool/test_writesame16_0blocks.c
+++ b/test-tool/test_writesame16_0blocks.c
@@ -27,6 +27,7 @@ void
 test_writesame16_0blocks(void)
 {
 	int ret;
+	unsigned char *buf = alloca(block_size);
 
 	CHECK_FOR_DATALOSS;
 	CHECK_FOR_SBC;
@@ -34,8 +35,9 @@ test_writesame16_0blocks(void)
 	logging(LOG_VERBOSE, LOG_BLANK_LINE);
 	logging(LOG_VERBOSE, "Test WRITESAME16 0-blocks at LBA==0 (WSNZ=%d)",
 		inq_bl->wsnz);
+	memset(buf, 0, block_size);
 	ret = writesame16(sd, 0,
-			  block_size, 0, 0, 0, 0, 0, NULL,
+			  block_size, 0, 0, 0, 0, 0, buf,
 			  EXPECT_STATUS_GOOD);
 	if (ret == -2) {
 		logging(LOG_NORMAL, "[SKIPPED] WRITESAME16 is not implemented.");
@@ -55,21 +57,21 @@ test_writesame16_0blocks(void)
 
 	logging(LOG_VERBOSE, "Test WRITESAME16 0-blocks one block past end-of-LUN");
 	ret = writesame16(sd, num_blocks + 1,
-			  block_size, inq_bl->wsnz, 0, 0, 0, 0, NULL,
+			  block_size, inq_bl->wsnz, 0, 0, 0, 0, buf,
 			  EXPECT_LBA_OOB);
 	CU_ASSERT_EQUAL(ret, 0);
 
 
 	logging(LOG_VERBOSE, "Test WRITESAME16 0-blocks at LBA==2^63");
 	ret = writesame16(sd, 0x8000000000000000ULL,
-			  block_size, inq_bl->wsnz, 0, 0, 0, 0, NULL,
+			  block_size, inq_bl->wsnz, 0, 0, 0, 0, buf,
 			  EXPECT_LBA_OOB);
 	CU_ASSERT_EQUAL(ret, 0);
 
 
 	logging(LOG_VERBOSE, "Test WRITESAME16 0-blocks at LBA==-1");
 	ret = writesame16(sd, -1,
-			  block_size, inq_bl->wsnz, 0, 0, 0, 0, NULL,
+			  block_size, inq_bl->wsnz, 0, 0, 0, 0, buf,
 			  EXPECT_LBA_OOB);
 	CU_ASSERT_EQUAL(ret, 0);
 }