diff --git a/firmware/drivers/fat.c b/firmware/drivers/fat.c
index 78aebd2e2b..022e3ebf90 100644
--- a/firmware/drivers/fat.c
+++ b/firmware/drivers/fat.c
@@ -265,8 +265,8 @@ static long cluster2sec(IF_MV2(struct bpb* fat_bpb,) long cluster)
 #else
     const long zerocluster = 2;
 #endif
-    long max_cluster = fat_bpb->totalsectors -
-        fat_bpb->firstdatasector / fat_bpb->bpb_secperclus + 1;
+    long max_cluster = (fat_bpb->totalsectors -
+        fat_bpb->firstdatasector) / fat_bpb->bpb_secperclus + 1;
     
     
     if (cluster > max_cluster)