diff --git a/pkgs/development/libraries/mbedtls/generic.nix b/pkgs/development/libraries/mbedtls/generic.nix
index 0b5082fe96f8..e986ea51ecb6 100644
--- a/pkgs/development/libraries/mbedtls/generic.nix
+++ b/pkgs/development/libraries/mbedtls/generic.nix
@@ -38,6 +38,9 @@ stdenv.mkDerivation rec {
 
   strictDeps = true;
 
+  # trivialautovarinit on clang causes test failures
+  hardeningDisable = lib.optional stdenv.cc.isClang "trivialautovarinit";
+
   postConfigure = lib.optionalString enableThreading ''
     perl scripts/config.pl set MBEDTLS_THREADING_C    # Threading abstraction layer
     perl scripts/config.pl set MBEDTLS_THREADING_PTHREAD    # POSIX thread wrapper layer for the threading layer.