diff --git a/tests/pkg_mbedtls/Makefile b/tests/pkg_mbedtls/Makefile
index 5634c3938c..033d86178a 100644
--- a/tests/pkg_mbedtls/Makefile
+++ b/tests/pkg_mbedtls/Makefile
@@ -3,6 +3,9 @@ include ../Makefile.tests_common
 USEPKG += mbedtls
 USEMODULE += mbedtls_entropy
 
+# entropy test keeps failing on this board due to low entropy
+TEST_ON_CI_BLACKLIST += samr21-xpro
+
 # Increase stack size of main thread.
 CFLAGS += -DTHREAD_STACKSIZE_MAIN=THREAD_STACKSIZE_LARGE