1 files changed, 6 insertions, 1 deletions

diff --git a/firmware/target/arm/as3525/sd-as3525.c b/firmware/target/arm/as3525/sd-as3525.c
index dea4a578cf..5cffced743 100644
--- a/firmware/target/arm/as3525/sd-as3525.c
+++ b/firmware/target/arm/as3525/sd-as3525.c
@@ -682,11 +682,16 @@ static int sd_transfer_sectors(IF_MD2(int drive,) unsigned long start,
             goto sd_transfer_error;
     }
 
-    if((start+count) > card_info[drive].numblocks)
+    if(count < 0) /* XXX: why is it signed ? */
     {
         ret = -20;
         goto sd_transfer_error;
     }
+    if((start+count) > card_info[drive].numblocks)
+    {
+        ret = -21;
+        goto sd_transfer_error;
+    }
 
     /* skip SanDisk OF */
     if (drive == INTERNAL_AS3525)