diff --git a/library/ccm.c b/library/ccm.c
index 0727a17..97c3c2a 100644
--- a/library/ccm.c
+++ b/library/ccm.c
@@ -143,7 +143,7 @@
 {
     int ret;
     unsigned char i;
-    unsigned char q = 16 - 1 - iv_len;
+    unsigned char q;
     size_t len_left, olen;
     unsigned char b[16];
     unsigned char y[16];
@@ -166,6 +166,8 @@
     if( add_len > 0xFF00 )
         return( MBEDTLS_ERR_CCM_BAD_INPUT );
 
+    q = 16 - 1 - (unsigned char) iv_len;
+
     /*
      * First block B_0:
      * 0        .. 0        flags
@@ -257,7 +259,7 @@
 
     while( len_left > 0 )
     {
-        unsigned char use_len = len_left > 16 ? 16 : len_left;
+        size_t use_len = len_left > 16 ? 16 : len_left;
 
         if( mode == CCM_ENCRYPT )
         {