diff --git a/pkgs/by-name/ul/ultimatepp/buildUppPackage.nix b/pkgs/by-name/ul/ultimatepp/buildUppPackage.nix
index 8f4d581..83f795b 100644
--- a/pkgs/by-name/ul/ultimatepp/buildUppPackage.nix
+++ b/pkgs/by-name/ul/ultimatepp/buildUppPackage.nix
@@ -59,7 +59,7 @@ stdenv.mkDerivation (self: {
       "$assemblies" \
       ${lib.escapeShellArg package} \
       ${buildMethod} \
-      -${if buildShared then "S" else "s"}uvr \
+      -${if buildShared then "S" else "s"}uvr "-H$NIX_BUILD_CORES" \
       ${flagsString} \
       $out/${output}
 
diff --git a/pkgs/by-name/ul/ultimatepp/package.nix b/pkgs/by-name/ul/ultimatepp/package.nix
index 8e4b8af..e117de2 100644
--- a/pkgs/by-name/ul/ultimatepp/package.nix
+++ b/pkgs/by-name/ul/ultimatepp/package.nix
@@ -94,8 +94,8 @@ in {
     if self.passthru.bootstrap then ''
     make -f umkMakefile -j $NIX_BUILD_CORES "$makeFlagsArray"
   '' else ''
-    ${lib.getExe' selfBootstrap "umk"} uppsrc ide ${buildMethod} -rvs
-    ${lib.getExe' selfBootstrap "umk"} uppsrc umk ${buildMethod} -rvs
+    ${lib.getExe' selfBootstrap "umk"} uppsrc ide ${buildMethod} -rvs "-H$NIX_BUILD_CORES"
+    ${lib.getExe' selfBootstrap "umk"} uppsrc umk ${buildMethod} -rvs "-H$NIX_BUILD_CORES"
   '') + ''
     runHook postBuild
   '';