1 files changed, 7 insertions, 4 deletions
diff --git a/Lib/configparser.py b/Lib/configparser.py
index 239fda60a02..18af1eadaad 100644
--- a/Lib/configparser.py
+++ b/Lib/configparser.py
@@ -1218,11 +1218,14 @@ class RawConfigParser(MutableMapping):
 
     def _validate_key_contents(self, key):
         """Raises an InvalidWriteError for any keys containing
-        delimiters or that match the section header pattern"""
+        delimiters or that begins with the section header pattern"""
         if re.match(self.SECTCRE, key):
-            raise InvalidWriteError("Cannot write keys matching section pattern")
-        if any(delim in key for delim in self._delimiters):
-            raise InvalidWriteError("Cannot write key that contains delimiters")
+            raise InvalidWriteError(
+                f"Cannot write key {key}; begins with section pattern")
+        for delim in self._delimiters:
+            if delim in key:
+                raise InvalidWriteError(
+                    f"Cannot write key {key}; contains delimiter {delim}")
 
     def _validate_value_types(self, *, section="", option="", value=""):
         """Raises a TypeError for illegal non-string values.