diff --git a/package_linter.py b/package_linter.py
index cd81ee0..9632807 100755
--- a/package_linter.py
+++ b/package_linter.py
@@ -474,10 +474,10 @@ class App(TestSuite):
         if not file_exists(check_process_file):
             return
 
-        if os.system("grep -q 'Level 5=1' %s" % check_process_file) == 0:
+        if os.system("grep -q 'Level 5=1' '%s'" % check_process_file) == 0:
             yield Error("Do not force Level 5=1 in check_process...")
 
-        if os.system("grep -q ' *Level [^5]=' %s" % check_process_file) == 0:
+        if os.system("grep -q ' *Level [^5]=' '%s'" % check_process_file) == 0:
             yield Warning("Setting Level x=y in check_process is obsolete / not relevant anymore")
 
     @test()
@@ -489,23 +489,23 @@ class App(TestSuite):
 
         has_is_public_arg = any(a["name"] == "is_public" for a in app.manifest["arguments"].get("install", []))
         if has_is_public_arg:
-            if os.system(r"grep -q '^\s*setup_public=1' %s" % check_process_file) != 0:
+            if os.system(r"grep -q '^\s*setup_public=1' '%s'" % check_process_file) != 0:
                 yield Warning("It looks like you forgot to enable setup_public test in check_process ?")
 
-            if os.system(r"grep -q '^\s*setup_private=1' %s" % check_process_file) != 0:
+            if os.system(r"grep -q '^\s*setup_private=1' '%s'" % check_process_file) != 0:
                 yield Warning("It looks like you forgot to enable setup_private test in check_process ?")
 
         has_path_arg = any(a["name"] == "path" for a in app.manifest["arguments"].get("install", []))
         if has_path_arg:
-            if os.system(r"grep -q '^\s*setup_sub_dir=1' %s" % check_process_file) != 0:
+            if os.system(r"grep -q '^\s*setup_sub_dir=1' '%s'" % check_process_file) != 0:
                 yield Warning("It looks like you forgot to enable setup_sub_dir test in check_process ?")
 
         if app.manifest.get("multi_instance") in [True, 1, "True", "true"]:
-            if os.system(r"grep -q '^\s*multi_instance=1' %s" % check_process_file) != 0:
+            if os.system(r"grep -q '^\s*multi_instance=1' '%s'" % check_process_file) != 0:
                 yield Warning("It looks like you forgot to enable multi_instance test in check_process ?")
 
         if app.scripts["backup"].exists:
-            if os.system(r"grep -q '^\s*backup_restore=1' %s" % check_process_file) != 0:
+            if os.system(r"grep -q '^\s*backup_restore=1' '%s'" % check_process_file) != 0:
                 yield Warning("It looks like you forgot to enable backup_restore test in check_process ?")
 
     @test()