diff --git a/mode_s.c b/mode_s.c
index e5e9c81..780e650 100644
--- a/mode_s.c
+++ b/mode_s.c
@@ -1774,7 +1774,7 @@ void detectModeS(uint16_t *m, uint32_t mlen) {
 
             // Skip this message if we are sure it's fine
             if (mm.crcok) {
-                j += (MODES_PREAMBLE_US+msglen)*2;
+                j += (MODES_PREAMBLE_US+msglen)*2 - 1;
             }
 
             // Pass data to the next layer
@@ -2092,4 +2092,4 @@ int decodeCPRrelative(struct aircraft *a, int fflag, int surface) {
 }
 //
 // ===================== Mode S detection and decoding  ===================
-//
\ No newline at end of file
+//