diff --git a/library/entropy.c b/library/entropy.c
index 1a7b9ab..49710de 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -27,6 +27,12 @@
 
 #if defined(MBEDTLS_ENTROPY_C)
 
+#if defined(MBEDTLS_TEST_NULL_ENTROPY)
+#warning "**** WARNING!  MBEDTLS_TEST_NULL_ENTROPY defined! ****"
+#warning "**** THIS BUILD HAS NO DEFINED ENTROPY SOURCES    ****"
+#warning "**** NOT SUITABLE FOR PRODUCTION                  ****"
+#endif
+
 #include "mbedtls/entropy.h"
 #include "mbedtls/entropy_poll.h"
 
@@ -73,7 +79,7 @@
     mbedtls_havege_init( &ctx->havege_data );
 #endif
 
-#if defined(MBEDTLS_TEST_WO_ENTROPY)
+#if defined(MBEDTLS_TEST_NULL_ENTROPY)
     mbedtls_entropy_add_source( ctx, mbedtls_zero_entropy_poll, NULL,
                                 1, MBEDTLS_ENTROPY_SOURCE_STRONG );
 #endif