diff --git a/library/debug.c b/library/debug.c
index 40286ac..d13eb5c 100644
--- a/library/debug.c
+++ b/library/debug.c
@@ -287,7 +287,7 @@
     else
     {
         int n;
-        for( n = ( bitlen - 1 ) / 8; n >= 0; n-- )
+        for( n = (int) ( bitlen - 1 ) / 8; n >= 0; n-- )
         {
             size_t limb_offset = n / sizeof( mbedtls_mpi_uint );
             size_t offset_in_limb = n % sizeof( mbedtls_mpi_uint );