diff --git a/include/mbedtls/entropy_poll.h b/include/mbedtls/entropy_poll.h
index a2acc1a..d7aa88c 100644
--- a/include/mbedtls/entropy_poll.h
+++ b/include/mbedtls/entropy_poll.h
@@ -46,7 +46,7 @@
 /**
  * \brief           Entropy poll callback that provides 0 entropy.
  */
-#if defined(MBEDTLS_TEST_WO_ENTROPY)
+#if defined(MBEDTLS_TEST_NULL_ENTROPY)
     int mbedtls_zero_entropy_poll( void *data,
                                 unsigned char *output, size_t len, size_t *olen );
 #endif