diff --git a/.github/workflows/manifold.yml b/.github/workflows/manifold.yml
index 4934e1f34..93fb746c7 100644
--- a/.github/workflows/manifold.yml
+++ b/.github/workflows/manifold.yml
@@ -139,10 +139,12 @@ jobs:
         cd build
         emcmake cmake -DCMAKE_BUILD_TYPE=Release -DMANIFOLD_PAR=${{matrix.parallelization}} .. && emmake make
     - name: Test WASM
+      if: matrix.parallelization == 'OFF'
       run: |
         cd build/test
         node ./manifold_test.js
     - name: Test examples
+      if: matrix.parallelization == 'OFF'
       run: |
         cd bindings/wasm/examples
         npm ci
diff --git a/flake.nix b/flake.nix
index ee78a62ee..3c999ac2b 100644
--- a/flake.nix
+++ b/flake.nix
@@ -134,11 +134,12 @@
           buildPhase = ''
             emmake make -j''${NIX_BUILD_CORES}
           '';
-          checkPhase = if doCheck then ''
-            cd test
-            node manifold_test.js
-            cd ../
-          '' else "";
+          checkPhase =
+            if doCheck then ''
+              cd test
+              node manifold_test.js
+              cd ../
+            '' else "";
           installPhase = ''
             mkdir -p $out
             cp bindings/wasm/manifold.* $out/
@@ -150,7 +151,11 @@
           manifold-tbb = manifold { };
           manifold-none = manifold { parallel = false; };
           manifold-js = manifold-emscripten { };
-          manifold-js-tbb = manifold-emscripten { parallel = true; };
+          manifold-js-tbb = manifold-emscripten {
+            parallel = true;
+            doCheck =
+              false;
+          };
           # but how should we make it work with other python versions?
           manifold3d = with pkgs.python3Packages; buildPythonPackage {
             pname = "manifold3d";