diff --git a/test-tool/test_writesame16_unmap.c b/test-tool/test_writesame16_unmap.c
index 3e3dfd9..206484f 100644
--- a/test-tool/test_writesame16_unmap.c
+++ b/test-tool/test_writesame16_unmap.c
@@ -30,7 +30,7 @@ test_writesame16_unmap(void)
 {
 	int i, ret;
 	unsigned int j;
-	unsigned char *buf = malloc(65536 * block_size);
+	unsigned char *buf;
 
 	CHECK_FOR_DATALOSS;
 	CHECK_FOR_THIN_PROVISIONING;
@@ -39,6 +39,7 @@ test_writesame16_unmap(void)
 
 	logging(LOG_VERBOSE, LOG_BLANK_LINE);
 	logging(LOG_VERBOSE, "Test WRITESAME16 of 1-256 blocks at the start of the LUN");
+	buf = malloc(65536 * block_size);
 	for (i = 1; i <= 256; i++) {
 		logging(LOG_VERBOSE, "Write %d blocks of 0xFF", i);
 		memset(buf, 0xff, i * block_size);