diff --git a/Tools/clinic/clinic.py b/Tools/clinic/clinic.py
index bf0fe5bed5a765d18e1a9fe2db9205bbab7b2d73..5ad4f879a33f7b76de609910249f0287afe14759 100755
--- a/Tools/clinic/clinic.py
+++ b/Tools/clinic/clinic.py
@@ -1628,10 +1628,16 @@ def parse_clinic_block(self, dsl_name):
         def is_stop_line(line):
             # make sure to recognize stop line even if it
             # doesn't end with EOL (it could be the very end of the file)
-            if not line.startswith(stop_line):
+            if line.startswith(stop_line):
+                remainder = line[len(stop_line):]
+                if remainder and not remainder.isspace():
+                    fail(f"Garbage after stop line: {remainder!r}")
+                return True
+            else:
+                # gh-92256: don't allow incorrectly formatted stop lines
+                if line.lstrip().startswith(stop_line):
+                    fail(f"Whitespace is not allowed before the stop line: {line!r}")
                 return False
-            remainder = line[len(stop_line):]
-            return (not remainder) or remainder.isspace()
 
         # consume body of program
         while self.input: