diff --git a/var/spack/repos/builtin/packages/petsc/package.py b/var/spack/repos/builtin/packages/petsc/package.py
index a934b0b8190..1ea72a1b949 100644
--- a/var/spack/repos/builtin/packages/petsc/package.py
+++ b/var/spack/repos/builtin/packages/petsc/package.py
@@ -574,12 +574,11 @@ def configure(self, spec, prefix):
 
     def build(self, spec, prefix):
         self.revert_kokkos_nvcc_wrapper()
-        # PETSc has its own way of doing parallel make.
-        make("V=1 MAKE_NP=%s" % make_jobs, parallel=False)
+        make("V=1")
 
     def install(self, spec, prefix):
         self.revert_kokkos_nvcc_wrapper()
-        make("install")
+        make("install", parallel=False)
 
         if self.run_tests:
             make('check PETSC_ARCH="" PETSC_DIR={0}'.format(prefix), parallel=False)
diff --git a/var/spack/repos/builtin/packages/slepc/package.py b/var/spack/repos/builtin/packages/slepc/package.py
index bcbafe4f731..ba4b9326ee6 100644
--- a/var/spack/repos/builtin/packages/slepc/package.py
+++ b/var/spack/repos/builtin/packages/slepc/package.py
@@ -148,7 +148,7 @@ def install(self, spec, prefix):
 
         python("configure", "--prefix=%s" % prefix, *options)
 
-        make("V=1 MAKE_NP=%s" % make_jobs, parallel=False)
+        make("V=1")
         if self.run_tests:
             make("test", parallel=False)