diff --git a/library/constant_time_internal.h b/library/constant_time_internal.h
index dabf720..44b74ae 100644
--- a/library/constant_time_internal.h
+++ b/library/constant_time_internal.h
@@ -85,12 +85,14 @@
 typedef uint64_t  mbedtls_ct_condition_t;
 typedef uint64_t  mbedtls_ct_uint_t;
 typedef int64_t   mbedtls_ct_int_t;
+#define MBEDTLS_CT_SIZE_64
 #define MBEDTLS_CT_TRUE  ((mbedtls_ct_condition_t) mbedtls_ct_compiler_opaque(UINT64_MAX))
 #else
 /* Pointer size <= 32-bit, and no 64-bit MPIs */
 typedef uint32_t  mbedtls_ct_condition_t;
 typedef uint32_t  mbedtls_ct_uint_t;
 typedef int32_t   mbedtls_ct_int_t;
+#define MBEDTLS_CT_SIZE_32
 #define MBEDTLS_CT_TRUE  ((mbedtls_ct_condition_t) mbedtls_ct_compiler_opaque(UINT32_MAX))
 #endif
 #define MBEDTLS_CT_FALSE ((mbedtls_ct_condition_t) mbedtls_ct_compiler_opaque(0))