diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 9557a377..8a1e5a9b 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -626,6 +626,8 @@ template <typename Char, typename Handler>
 FMT_CONSTEXPR const Char* parse_chrono_format(const Char* begin,
                                               const Char* end,
                                               Handler&& handler) {
+  if (begin == end || *begin == '}') return begin;
+  if (*begin != '%') FMT_THROW(format_error("invalid format"));
   auto ptr = begin;
   while (ptr != end) {
     auto c = *ptr;
diff --git a/test/chrono-test.cc b/test/chrono-test.cc
index 44eccac8..f986c203 100644
--- a/test/chrono-test.cc
+++ b/test/chrono-test.cc
@@ -507,6 +507,10 @@ TEST(chrono_test, invalid_specs) {
                    "invalid format");
   EXPECT_THROW_MSG((void)fmt::format(runtime("{:%Oq}"), sec), fmt::format_error,
                    "invalid format");
+  EXPECT_THROW_MSG((void)fmt::format(runtime("{:abc}"), sec), fmt::format_error,
+                   "invalid format");
+  EXPECT_THROW_MSG((void)fmt::format(runtime("{:.2f}"), sec), fmt::format_error,
+                   "invalid format");
 }
 
 auto format_tm(const std::tm& time, fmt::string_view spec,