diff --git a/pyModeS/decoder/bds/bds40.py b/pyModeS/decoder/bds/bds40.py
index 4908976..a473da5 100644
--- a/pyModeS/decoder/bds/bds40.py
+++ b/pyModeS/decoder/bds/bds40.py
@@ -47,6 +47,12 @@ def is40(msg):
 
     if wrongstatus(d, 27, 28, 39):
         return False
+    
+    if wrongstatus(d, 48, 49, 51):
+        return False
+    
+    if wrongstatus(d, 54, 55, 56):
+        return False
 
     # bits 40-47 and 52-53 shall all be zero
 
@@ -55,6 +61,7 @@ def is40(msg):
 
     if bin2int(d[51:53]) != 0:
         return False
+    
 
     return True