diff --git a/library/ccm.c b/library/ccm.c
index e6ca588..424ee77 100644
--- a/library/ccm.c
+++ b/library/ccm.c
@@ -175,7 +175,7 @@
     if( iv_len < 7 || iv_len > 13 )
         return( MBEDTLS_ERR_CCM_BAD_INPUT );
 
-    if( add_len > 0xFF00 )
+    if( add_len >= 0xFF00 )
         return( MBEDTLS_ERR_CCM_BAD_INPUT );
 
     q = 16 - 1 - (unsigned char) iv_len;