diff --git a/libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c b/libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c
index f1f735ab8f..a3407e9edf 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c
+++ b/libraries/AP_HAL_ChibiOS/hwdef/common/bouncebuffer.c
@@ -48,7 +48,13 @@ void bouncebuffer_init(struct bouncebuffer_t **bouncebuffer, uint32_t prealloc_b
 bool bouncebuffer_setup_read(struct bouncebuffer_t *bouncebuffer, uint8_t **buf, uint32_t size)
 {
     if (!bouncebuffer || mem_is_dma_safe(*buf, size, bouncebuffer->on_axi_sram)) {
-        // nothing needs to be done
+#if defined(STM32H7)
+        /*
+          on H7 the cache needs invalidating before a read to ensure
+          there is no stale data in the buffer
+         */
+        stm32_cacheBufferInvalidate(*buf, (size+31)&~31);
+#endif
         return true;
     }
     osalDbgAssert((bouncebuffer->busy == false), "bouncebuffer read");        
@@ -97,7 +103,12 @@ void bouncebuffer_finish_read(struct bouncebuffer_t *bouncebuffer, const uint8_t
 bool bouncebuffer_setup_write(struct bouncebuffer_t *bouncebuffer, const uint8_t **buf, uint32_t size)
 {
     if (!bouncebuffer || mem_is_dma_safe(*buf, size, bouncebuffer->on_axi_sram)) {
-        // nothing needs to be done
+#if defined(STM32H7)
+        /*
+          on H7 we need to flush any pending writes to memory before the DMA operation
+         */
+        stm32_cacheBufferFlush(*buf, (size+31)&~31);
+#endif
         return true;
     }
     osalDbgAssert((bouncebuffer->busy == false), "bouncebuffer write");        
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/common/malloc.c b/libraries/AP_HAL_ChibiOS/hwdef/common/malloc.c
index bf39aa6d44..97b837b12a 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/common/malloc.c
+++ b/libraries/AP_HAL_ChibiOS/hwdef/common/malloc.c
@@ -635,7 +635,7 @@ bool mem_is_dma_safe(const void *addr, uint32_t size, bool filesystem_op)
         // use bouncebuffer for all non FS ops on H7
         return false;
     }
-    if (((uint32_t)addr) & 0x1F) {
+    if ((((uint32_t)addr) & 0x1F) != 0 || (size & 0x1F) != 0) {
         return false;
     }
     if (filesystem_op) {