diff --git a/lib/utils/mu-error.hh b/lib/utils/mu-error.hh
index 8baea197..c34bd255 100644
--- a/lib/utils/mu-error.hh
+++ b/lib/utils/mu-error.hh
@@ -41,6 +41,7 @@ struct Error final : public std::exception {
 		Query,
 		SchemaMismatch,
 		Store,
+		AssertionFailure
 	};
 
 	/**
@@ -50,6 +51,7 @@ struct Error final : public std::exception {
 	 * #param msgarg the error diecription
 	 */
 	Error(Code codearg, const std::string& msgarg) : code_{codearg}, what_{msgarg} {}
+	Error(Code codearg, std::string&& msgarg) : code_{codearg}, what_{std::move(msgarg)} {}
 
 	/**
 	 * Build an error from an error-code and a format string
diff --git a/lib/utils/mu-result.hh b/lib/utils/mu-result.hh
index 8e304fdc..58b2b322 100644
--- a/lib/utils/mu-result.hh
+++ b/lib/utils/mu-result.hh
@@ -76,7 +76,29 @@ Err(const Error& err)
 	return tl::unexpected(err);
 }
 
-} // namespace Mu
 
+/*
+ * convenience
+ */
+
+static inline tl::unexpected<Error>
+Err(Error::Code errcode, std::string&& msg="")
+{
+	return Err(Error{errcode, std::move(msg)});
+}
+
+__attribute__((format(printf, 2, 0)))
+static inline tl::unexpected<Error>
+Err(Error::Code errcode, const char* frm, ...)
+{
+	va_list args;
+	va_start(args, frm);
+	auto str{vformat(frm, args)};
+	va_end(args);
+
+	return Err(errcode, std::move(str));
+}
+
+}// namespace Mu
 
 #endif /* MU_RESULT_HH__ */