1 files changed, 6 insertions, 1 deletions

diff --git a/flash/extract/extract.c b/flash/extract/extract.c
index 31e223a546..2a8a7b3ec7 100644
--- a/flash/extract/extract.c
+++ b/flash/extract/extract.c
@@ -113,7 +113,12 @@ int main(int argc, char* argv[])
 
         // generate checksum
         for (i=0; i<uiSize; i++)
-                usChecksum += aImage[uiStart + i];
+        {
+                UINT8 byte;
+                byte = aImage[uiStart + i];
+                byte = ~((byte >> 1) | ((byte << 7) & 0x80)); /* poor man's ROR */
+                usChecksum += byte;
+        }
 
         // make header
         Write32(aHeader + 2, usChecksum); // checksum in 5th and 6th byte