diff --git a/pkgs/development/python-modules/optuna/default.nix b/pkgs/development/python-modules/optuna/default.nix
index 64ed54cafbe..aa61b18291d 100644
--- a/pkgs/development/python-modules/optuna/default.nix
+++ b/pkgs/development/python-modules/optuna/default.nix
@@ -84,6 +84,7 @@ buildPythonPackage rec {
   '';
 
   meta = with lib; {
+    broken = true;  # Dashboard broken, other build failures.
     description = "A hyperparameter optimization framework";
     homepage = "https://optuna.org/";
     license = licenses.mit;
diff --git a/pkgs/development/python-modules/tensorflow-probability/default.nix b/pkgs/development/python-modules/tensorflow-probability/default.nix
index a89c6fa307e..91880562eb3 100644
--- a/pkgs/development/python-modules/tensorflow-probability/default.nix
+++ b/pkgs/development/python-modules/tensorflow-probability/default.nix
@@ -122,9 +122,10 @@ in buildPythonPackage {
   '';
 
   meta = with lib; {
+    broken = true;  # tf-probability 0.8.0 is not compatible with tensorflow 2.3.2
     description = "Library for probabilistic reasoning and statistical analysis";
     homepage = "https://www.tensorflow.org/probability/";
     license = licenses.asl20;
-    maintainers = with maintainers; [ timokau ];
+    maintainers = with maintainers; [];  # This package is maintainerless.
   };
 }
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 75f8c6ffc5d..3b74487a444 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -27876,6 +27876,7 @@ in
 
   mxnet = callPackage ../applications/science/math/mxnet {
     inherit (linuxPackages) nvidia_x11;
+    stdenv = gcc9Stdenv;
   };
 
   wxmaxima = callPackage ../applications/science/math/wxmaxima { wxGTK = wxGTK30; };