diff --git a/library/entropy.c b/library/entropy.c
index 49710de..282640f 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -80,7 +80,7 @@
 #endif
 
 #if defined(MBEDTLS_TEST_NULL_ENTROPY)
-    mbedtls_entropy_add_source( ctx, mbedtls_zero_entropy_poll, NULL,
+    mbedtls_entropy_add_source( ctx, mbedtls_null_entropy_poll, NULL,
                                 1, MBEDTLS_ENTROPY_SOURCE_STRONG );
 #endif