diff --git a/library/entropy.c b/library/entropy.c
index cdbd35c..381f730 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -73,6 +73,11 @@
     mbedtls_havege_init( &ctx->havege_data );
 #endif
 
+#if defined(MBEDTLS_TEST_WO_ENTROPY)
+    mbedtls_entropy_add_source( ctx, mbedtls_zero_entropy_poll, NULL,
+                                1, MBEDTLS_ENTROPY_SOURCE_STRONG );
+#endif
+
 #if !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES)
 #if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
     mbedtls_entropy_add_source( ctx, mbedtls_platform_entropy_poll, NULL,