diff --git a/include/mbedtls/cipher.h b/include/mbedtls/cipher.h
index 2596baa..815b5bb 100644
--- a/include/mbedtls/cipher.h
+++ b/include/mbedtls/cipher.h
@@ -480,7 +480,7 @@
     if (info == NULL) {
         return 0;
     } else {
-        return info->MBEDTLS_PRIVATE(key_bitlen) << MBEDTLS_KEY_BITLEN_SHIFT;
+        return ((size_t) info->MBEDTLS_PRIVATE(key_bitlen)) << MBEDTLS_KEY_BITLEN_SHIFT;
     }
 }