diff --git a/pkgs/applications/science/math/mxnet/default.nix b/pkgs/applications/science/math/mxnet/default.nix
index a3043bcf695..990d3f1a5d5 100644
--- a/pkgs/applications/science/math/mxnet/default.nix
+++ b/pkgs/applications/science/math/mxnet/default.nix
@@ -34,11 +34,14 @@ stdenv.mkDerivation rec {
   postPatch = ''
     substituteInPlace 3rdparty/mkldnn/tests/CMakeLists.txt \
       --replace "/bin/bash" "${bash}/bin/bash"
+
+    # Build against the system version of OpenMP. 
+    # https://github.com/apache/incubator-mxnet/pull/12160
+    rm -rf 3rdparty/openmp
   '';
 
-  installPhase = ''
-    install -Dm755 libmxnet.so $out/lib/libmxnet.so
-    cp -r ../include $out
+  postInstall = ''
+    rm "$out"/lib/*.a
   '';
 
   enableParallelBuilding = true;
diff --git a/pkgs/top-level/python-packages.nix b/pkgs/top-level/python-packages.nix
index f74f9ace2fd..5ef8626d72e 100644
--- a/pkgs/top-level/python-packages.nix
+++ b/pkgs/top-level/python-packages.nix
@@ -1788,6 +1788,13 @@ in {
 
     doCheck = !isPy3k;
 
+    postPatch = ''
+      substituteInPlace python/setup.py \
+      --replace "graphviz<0.9.0" "graphviz<0.10.0" \
+      --replace "numpy<=1.15.0" "numpy<1.16.0" \
+      --replace "requests<2.19.0" "requests<2.20.0"
+    '';
+
     preConfigure = ''
       cd python
     '';
@@ -7937,11 +7944,11 @@ in {
 
   graphviz = buildPythonPackage rec {
     name = "graphviz-${version}";
-    version = "0.5.2";
+    version = "0.9";
 
     src = pkgs.fetchurl {
       url = "mirror://pypi/g/graphviz/${name}.zip";
-      sha256 = "0jh31nlm0qbxwylhdkwnb69pcjlc5z03fcfbs0gvgzp3hfrngsk0";
+      sha256 = "14r9brj4r31b3qy1nnn34v3l4h0n39bqxg9sn2fz4p3pp5mglnl6";
     };
 
     propagatedBuildInputs = [ pkgs.graphviz ];