diff --git a/clang/utils/creduce-clang-crash.py b/clang/utils/creduce-clang-crash.py
--- a/clang/utils/creduce-clang-crash.py
+++ b/clang/utils/creduce-clang-crash.py
@@ -30,6 +30,7 @@
     print(*args, **kwargs)
 
 def check_file(fname):
+  fname = os.path.normpath(fname)
   if not os.path.isfile(fname):
     sys.exit("ERROR: %s does not exist" % (fname))
   return fname
@@ -40,6 +41,8 @@
   or absolute path to cmd_dir/cmd_name.
   """
   if cmd_path:
+    # Make the path absolute so the creduce test can be run from any directory.
+    cmd_path = os.path.abspath(cmd_path)
     cmd = find_executable(cmd_path)
     if cmd:
       return cmd