Index: utils/UpdateTestChecks/common.py
===================================================================
--- utils/UpdateTestChecks/common.py
+++ utils/UpdateTestChecks/common.py
@@ -264,3 +264,12 @@
 def add_analyze_checks(output_lines, comment_marker, prefix_list, func_dict, func_name):
   check_label_format = '{} %s-LABEL: \'%s\''.format(comment_marker)
   add_checks(output_lines, comment_marker, prefix_list, func_dict, func_name, check_label_format, False, True)
+
+def verify_filecheck_prefixes(fc_cmd):
+  fc_cmd_parts = fc_cmd.split()
+  for part in fc_cmd_parts:
+    if "check-prefix=" in part:
+      prefix = part.split('=')[1]
+      if ',' in prefix:
+        print('WARNING: Prefix \'%s\' is invalid. Did you mean \'--check-prefixes=%s\'?' %
+              (prefix, prefix), file=sys.stderr)
Index: utils/update_llc_test_checks.py
===================================================================
--- utils/update_llc_test_checks.py
+++ utils/update_llc_test_checks.py
@@ -89,6 +89,8 @@
       filecheck_cmd = ''
       if len(commands) > 1:
         filecheck_cmd = commands[1]
+      common.verify_filecheck_prefixes(filecheck_cmd)
+
       if not llc_cmd.startswith('llc '):
         print('WARNING: Skipping non-llc RUN line: ' + l, file=sys.stderr)
         continue
Index: utils/update_mir_test_checks.py
===================================================================
--- utils/update_mir_test_checks.py
+++ utils/update_mir_test_checks.py
@@ -122,6 +122,7 @@
         commands = [cmd.strip() for cmd in l.split('|', 1)]
         llc_cmd = commands[0]
         filecheck_cmd = commands[1] if len(commands) > 1 else ''
+        common.verify_filecheck_prefixes(filecheck_cmd)
 
         if not llc_cmd.startswith('llc '):
             warn('Skipping non-llc RUN line: {}'.format(l), test_file=test)