diff --git a/src/coreclr/tests/scripts/run-pmi-diffs.py b/src/coreclr/tests/scripts/run-pmi-diffs.py
index bfaaec50550f80..d1e5954b931460 100755
--- a/src/coreclr/tests/scripts/run-pmi-diffs.py
+++ b/src/coreclr/tests/scripts/run-pmi-diffs.py
@@ -148,14 +148,14 @@ def validate_args(args):
     coreclr_setup_args.verify(args,
                               "diff_root",
                               lambda directory: os.path.isdir(directory) if directory is not None else True,
-                              "Base root is not a valid directory",
+                              "Diff root is not a valid directory",
                               modify_arg=lambda directory: nth_dirname(os.path.abspath(sys.argv[0]), 3) if directory is None else os.path.abspath(directory))
 
     coreclr_setup_args.verify(args,
                               "scratch_root",
-                              lambda directory: os.path.isdir(directory) if directory is not None else True,
-                              "Base root is not a valid directory",
-                              modify_arg=lambda directory: nth_dirname(os.path.abspath(sys.argv[0]), 3) if directory is None else os.path.abspath(directory))
+                              lambda unused: True,
+                              "Error setting scratch_root",
+                              modify_arg=lambda directory: os.path.join(coreclr_setup_args.diff_root, '_', 'pmi') if directory is None else os.path.abspath(directory))
 
     coreclr_setup_args.verify(args,
                               "skip_baseline_build",