diff --git a/lib/tests/test-mu-maildir.cc b/lib/tests/test-mu-maildir.cc
index 62cd3215..ded4e191 100644
--- a/lib/tests/test-mu-maildir.cc
+++ b/lib/tests/test-mu-maildir.cc
@@ -517,7 +517,7 @@ test_maildir_move_vanilla()
 }
 
 static void
-test_maildir_move_gio()
+test_maildir_move_remote()
 {
 	test_maildir_move(true/*assume_remote*/);
 }
@@ -549,7 +549,7 @@ main(int argc, char* argv[])
 
 	g_test_add_func("/maildir/link", test_maildir_link);
 	g_test_add_func("/maildir/move-vanilla", test_maildir_move_vanilla);
-	g_test_add_func("/maildir/aildir-move-gio", test_maildir_move_gio);
+	g_test_add_func("/maildir/move-remote", test_maildir_move_remote);
 
 	return g_test_run();
 }
diff --git a/lib/utils/mu-logger.cc b/lib/utils/mu-logger.cc
index 258643c9..04c6611a 100644
--- a/lib/utils/mu-logger.cc
+++ b/lib/utils/mu-logger.cc
@@ -211,7 +211,7 @@ test_logger_threads(void)
 		threads.emplace_back(
 			std::thread([n,&running]{
 				while (running) {
-					mu_debug("log message from thread <{}>", n);
+					//mu_debug("log message from thread <{}>", n);
 					std::this_thread::yield();
 				}
 			}));
diff --git a/lib/utils/mu-regex.cc b/lib/utils/mu-regex.cc
index cfdeccf0..81276952 100644
--- a/lib/utils/mu-regex.cc
+++ b/lib/utils/mu-regex.cc
@@ -33,8 +33,15 @@ test_regex_match()
 	auto rx = Regex::make("a.*b.c");
 	assert_valid_result(rx);
 
+	assert_equal(mu_format("{}", *rx), "/a.*b.c/");
+
 	g_assert_true(rx->matches("axxxxxbqc"));
 	g_assert_false(rx->matches("axxxxxbqqc"));
+
+	{ // unset matches nothing.
+		Regex rx2;
+		g_assert_false(rx2.matches(""));
+	}
 }
 
 
@@ -43,7 +50,6 @@ test_regex_match2()
 {
 	Regex rx;
 	{
-
 		std::string foo = "h.llo";
 		rx = unwrap(Regex::make(foo.c_str()));
 	}
@@ -61,16 +67,37 @@ test_regex_replace()
 	{
 		auto rx = Regex::make("f.o");
 		assert_valid_result(rx);
-		assert_equal(rx->replace("foobar", "cuux"), "cuuxbar");
+		assert_equal(rx->replace("foobar", "cuux").value_or("error"), "cuuxbar");
 	}
 
 	{
 		auto rx = Regex::make("f.o", G_REGEX_MULTILINE);
 		assert_valid_result(rx);
-		assert_equal(rx->replace("foobar\nfoobar", "cuux"), "cuuxbar\ncuuxbar");
+		assert_equal(rx->replace("foobar\nfoobar", "cuux").value_or("error"),
+			     "cuuxbar\ncuuxbar");
 	}
 }
 
+
+static void
+test_regex_fail()
+{
+	allow_warnings();
+
+	{ // unset rx can't replace / error.
+		Regex rx;
+		assert_equal(mu_format("{}", rx), "//");
+		g_assert_false(!!rx.replace("foo", "bar"));
+	}
+
+	{
+		auto rx = Regex::make("(");
+		g_assert_false(!!rx);
+
+	}
+
+}
+
 int
 main(int argc, char* argv[])
 {
@@ -79,6 +106,7 @@ main(int argc, char* argv[])
 	g_test_add_func("/regex/match", test_regex_match);
 	g_test_add_func("/regex/match2", test_regex_match2);
 	g_test_add_func("/regex/replace", test_regex_replace);
+	g_test_add_func("/regex/fail", test_regex_fail);
 
 	return g_test_run();
 }
diff --git a/lib/utils/mu-regex.hh b/lib/utils/mu-regex.hh
index 409c7d3a..c5fd4a00 100644
--- a/lib/utils/mu-regex.hh
+++ b/lib/utils/mu-regex.hh
@@ -52,8 +52,7 @@ struct Regex {
 	 */
 	static Result<Regex> make(const std::string& ptrn,
 				  GRegexCompileFlags cflags = G_REGEX_DEFAULT,
-				  GRegexMatchFlags mflags = G_REGEX_MATCH_DEFAULT)
-		noexcept try {
+				  GRegexMatchFlags mflags = G_REGEX_MATCH_DEFAULT) noexcept try {
 		return Regex(ptrn.c_str(), cflags, mflags);
 	} catch (const Error& err) {
 		return Err(err);
@@ -146,20 +145,24 @@ struct Regex {
 	}
 
 	/**
-	 * Replace all occurences of @this regexp in some string with a
+	 * Replace all occurrences of @this regexp in some string with a
 	 * replacement string
 	 *
 	 * @param str some string
 	 * @param repl replacement string
 	 *
-	 * @return string
+	 * @return string or error
 	 */
-	std::string replace(const std::string& str, const std::string& repl) {
-		char *s{g_regex_replace(rx_, str.c_str(), str.length(), 0,
-					repl.c_str(), G_REGEX_MATCH_DEFAULT, {})};
-		if (!s)
-			throw Err(Error::Code::InvalidArgument, "error in Regex::replace");
-		return to_string_gchar(std::move(s));
+	Result<std::string> replace(const std::string& str, const std::string& repl) const {
+		GError *gerr{};
+
+		if (!rx_)
+			return Err(Error::Code::InvalidArgument, "missing regexp");
+		else if (auto&& s{g_regex_replace(rx_, str.c_str(), str.length(), 0,
+					     repl.c_str(), G_REGEX_MATCH_DEFAULT, &gerr)}; !s)
+			return Err(Error::Code::InvalidArgument, &gerr, "error in Regex::replace");
+		else
+			return Ok(to_string_gchar(std::move(s)));
 	}
 
 	const GRegex* g_regex() const { return rx_; }
@@ -168,11 +171,11 @@ private:
 	Regex(const char *ptrn, GRegexCompileFlags cflags, GRegexMatchFlags mflags) {
 		GError *err{};
 		if (rx_ = g_regex_new(ptrn, cflags, mflags, &err); !rx_)
-			throw Err(Error::Code::InvalidArgument, &err,
-				  "invalid regexp: '{}'", ptrn);
+			throw Error{Error::Code::InvalidArgument, &err,
+				"invalid regexp: '{}'", ptrn};
 	}
 
-	GRegex *rx_;
+	GRegex *rx_{};
 };
 
 static inline std::string format_as(const Regex& rx) {
diff --git a/lib/utils/tests/test-utils.cc b/lib/utils/tests/test-utils.cc
index 7b34aad1..993c875c 100644
--- a/lib/utils/tests/test-utils.cc
+++ b/lib/utils/tests/test-utils.cc
@@ -319,8 +319,6 @@ test_summarize(void)
 			"fortification by the Bais raja Sathna. ");
 }
 
-
-
 int
 main(int argc, char* argv[])
 {
diff --git a/mu/mu-cmd-view.cc b/mu/mu-cmd-view.cc
index c80e46f0..3ddd78e1 100644
--- a/mu/mu-cmd-view.cc
+++ b/mu/mu-cmd-view.cc
@@ -251,7 +251,7 @@ test_view_plain()
 
 	// silly hack to avoid locale  diffs
 	auto rx = unwrap(Regex::make("^Date:.*", G_REGEX_MULTILINE));
-	output.standard_out = rx.replace(output.standard_out, "Date: xxx");
+	output.standard_out = unwrap(rx.replace(output.standard_out, "Date: xxx"));
 
 	g_assert_true(output.standard_err.empty());
 	assert_equal(output.standard_out,
@@ -273,7 +273,7 @@ test_view_html()
 	auto output{*res};
 
 	auto rx = unwrap(Regex::make("^Date:.*", G_REGEX_MULTILINE));
-	output.standard_out = rx.replace(output.standard_out, "Date: xxx");
+	output.standard_out = unwrap(rx.replace(output.standard_out, "Date: xxx"));
 
 	g_assert_true(output.standard_err.empty());
 	assert_equal(output.standard_out,