diff --git a/pkgs/applications/science/logic/symbiyosys/default.nix b/pkgs/applications/science/logic/symbiyosys/default.nix
index 1f2ad4634de2..118bb8ecd206 100644
--- a/pkgs/applications/science/logic/symbiyosys/default.nix
+++ b/pkgs/applications/science/logic/symbiyosys/default.nix
@@ -31,6 +31,9 @@ stdenv.mkDerivation {
 
     substituteInPlace sbysrc/sby_core.py \
       --replace '##yosys-program-prefix##' '"${yosys}/bin/"'
+
+    substituteInPlace sbysrc/sby.py \
+      --replace '/usr/bin/env python3' '${python3}/bin/python'
   '';
 
   buildPhase = "true";
diff --git a/pkgs/development/python-modules/nmigen/default.nix b/pkgs/development/python-modules/nmigen/default.nix
index 4a2327bf9288..ca898b988c71 100644
--- a/pkgs/development/python-modules/nmigen/default.nix
+++ b/pkgs/development/python-modules/nmigen/default.nix
@@ -38,13 +38,6 @@ buildPythonPackage rec {
     export SETUPTOOLS_SCM_PRETEND_VERSION="${realVersion}"
   '';
 
-  # Fail b/c can't find sby (symbiyosys) executable, which should be on path.
-  disabledTests = [
-    "test_distance"
-    "test_reversible"
-    "FIFOFormalCase"
-  ];
-
   meta = with lib; {
     description = "A refreshed Python toolbox for building complex digital hardware";
     homepage = "https://nmigen.info/nmigen";