diff --git a/tests/unit/test-block-iothread.c b/tests/unit/test-block-iothread.c
index 3f866a35c6..8cf172cb7a 100644
--- a/tests/unit/test-block-iothread.c
+++ b/tests/unit/test-block-iothread.c
@@ -89,7 +89,7 @@ static void test_sync_op_pread(BdrvChild *c)
 
 static void test_sync_op_pwrite(BdrvChild *c)
 {
-    uint8_t buf[512];
+    uint8_t buf[512] = { 0 };
     int ret;
 
     /* Success */
@@ -117,7 +117,7 @@ static void test_sync_op_blk_pread(BlockBackend *blk)
 
 static void test_sync_op_blk_pwrite(BlockBackend *blk)
 {
-    uint8_t buf[512];
+    uint8_t buf[512] = { 0 };
     int ret;
 
     /* Success */
@@ -141,7 +141,7 @@ static void test_sync_op_load_vmstate(BdrvChild *c)
 
 static void test_sync_op_save_vmstate(BdrvChild *c)
 {
-    uint8_t buf[512];
+    uint8_t buf[512] = { 0 };
     int ret;
 
     /* Error: Driver does not support snapshots */