diff --git a/include/toml++/impl/parser.inl b/include/toml++/impl/parser.inl
index 89682f28..f9b03c8e 100644
--- a/include/toml++/impl/parser.inl
+++ b/include/toml++/impl/parser.inl
@@ -3157,6 +3157,11 @@ TOML_IMPL_NAMESPACE_START
 				if (*cp == U']')
 					set_error_and_return_default("tables with blank bare keys are explicitly prohibited"sv);
 
+				if (!is_bare_key_character(*cp) && !is_string_delimiter(*cp))
+					set_error_and_return_default("expected bare key starting character or string delimiter, saw '"sv,
+												 to_sv(*cp),
+												 "'"sv);
+
 				// get the actual key
 				start_recording();
 				parse_key();
diff --git a/tests/parsing_tables.cpp b/tests/parsing_tables.cpp
index 417427e5..fa21bf2e 100644
--- a/tests/parsing_tables.cpp
+++ b/tests/parsing_tables.cpp
@@ -20,6 +20,11 @@ TEST_CASE("parsing - tables")
 						   });
 	parsing_should_fail(FILE_LINE_ARGS, "[]"sv);
 
+	parsing_should_fail(FILE_LINE_ARGS, "[[[1]]]"sv);
+	parsing_should_fail(FILE_LINE_ARGS, "[[[a]]]"sv);
+	parsing_should_fail(FILE_LINE_ARGS, "[[[]]"sv);
+	parsing_should_fail(FILE_LINE_ARGS, "[[="sv);
+
 	// "Under that, and until the next header or EOF, are the key/values of that table.
 	//  Key/value pairs within tables are not guaranteed to be in any specific order."
 	parsing_should_succeed(FILE_LINE_ARGS,
diff --git a/toml.hpp b/toml.hpp
index 91f99d9f..fc12d078 100644
--- a/toml.hpp
+++ b/toml.hpp
@@ -15741,6 +15741,11 @@ TOML_IMPL_NAMESPACE_START
 				if (*cp == U']')
 					set_error_and_return_default("tables with blank bare keys are explicitly prohibited"sv);
 
+				if (!is_bare_key_character(*cp) && !is_string_delimiter(*cp))
+					set_error_and_return_default("expected bare key starting character or string delimiter, saw '"sv,
+												 to_sv(*cp),
+												 "'"sv);
+
 				// get the actual key
 				start_recording();
 				parse_key();