diff --git a/library/aes.c b/library/aes.c
index 1c743f9..0543cd7 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -1298,7 +1298,7 @@
 
     n = *iv_off;
 
-    if( n > 16 )
+    if( n > 15 )
         return( MBEDTLS_ERR_AES_BAD_INPUT_DATA );
 
     if( mode == MBEDTLS_AES_DECRYPT )
@@ -1394,7 +1394,7 @@
 
     n = *iv_off;
 
-    if( n > 16 )
+    if( n > 15 )
         return( MBEDTLS_ERR_AES_BAD_INPUT_DATA );
 
     while( length-- )