diff --git a/pkgs/os-specific/linux/acpi-call/default.nix b/pkgs/os-specific/linux/acpi-call/default.nix
index d7c9e2c3695..f9615da0c2f 100644
--- a/pkgs/os-specific/linux/acpi-call/default.nix
+++ b/pkgs/os-specific/linux/acpi-call/default.nix
@@ -10,16 +10,14 @@ stdenv.mkDerivation {
   };
   
   preBuild = ''
-    kernelVersion=$(cd ${kernel}/lib/modules && ls)
     sed -e 's/break/true/' -i test_off.sh
     sed -e 's@/bin/bash@.bin/sh@' -i test_off.sh
-    sed -e "s@/lib/modules/\$(.*)@${kernel}/lib/modules/$kernelVersion@" -i Makefile
+    sed -e "s@/lib/modules/\$(.*)@${kernel}/lib/modules/${kernel.version}@" -i Makefile
   '';
  
   installPhase = ''
-    kernelVersion=$(cd ${kernel}/lib/modules && ls)
-    ensureDir $out/lib/modules/$kernelVersion/misc
-    cp acpi_call.ko $out/lib/modules/$kernelVersion/misc
+    ensureDir $out/lib/modules/${kernel.version}/misc
+    cp acpi_call.ko $out/lib/modules/${kernel.version}/misc
     ensureDir $out/bin
     cp test_off.sh $out/bin/test_discrete_video_off.sh
   '';
diff --git a/pkgs/os-specific/linux/bbswitch/default.nix b/pkgs/os-specific/linux/bbswitch/default.nix
index a8f8a9d33ef..7c5752b4e34 100644
--- a/pkgs/os-specific/linux/bbswitch/default.nix
+++ b/pkgs/os-specific/linux/bbswitch/default.nix
@@ -17,14 +17,13 @@ stdenv.mkDerivation {
   preBuild = ''
     kernelVersion=$(cd ${kernel}/lib/modules && ls)
     substituteInPlace Makefile \
-      --replace "\$(shell uname -r)" "$kernelVersion" \
+      --replace "\$(shell uname -r)" "${kernel.version}" \
       --replace "/lib/modules" "${kernel}/lib/modules"
   '';
  
   installPhase = ''
-    kernelVersion=$(cd ${kernel}/lib/modules && ls)
-    ensureDir $out/lib/modules/$kernelVersion/misc
-    cp bbswitch.ko $out/lib/modules/$kernelVersion/misc
+    ensureDir $out/lib/modules/${kernel.version}/misc
+    cp bbswitch.ko $out/lib/modules/${kernel.version}/misc
 
     ensureDir $out/bin
     tee $out/bin/discrete_vga_poweroff << EOF