diff --git a/src/error.cc b/src/error.cc
index 9448836..5831a43 100644
--- a/src/error.cc
+++ b/src/error.cc
@@ -5,7 +5,7 @@ static const char* messages[] = {
 	"Need to exit",
 	"Bad command-line arguments",
 	"Integer overflow",
-	"Standard error",
+	nullptr, /* standard error: call stderror */
 	"End of file",
 	"libogg error",
 	"Bad magic number",
@@ -19,8 +19,10 @@ static const char* messages[] = {
 
 const char* ot::error_message(ot::status code)
 {
-if (code >= ot::status::sentinel)
-	return nullptr;
-auto index = static_cast<size_t>(code);
-return messages[index];
+	if (code == ot::status::standard_error)
+		return strerror(errno);
+	if (code >= ot::status::sentinel)
+		return nullptr;
+	auto index = static_cast<size_t>(code);
+	return messages[index];
 }
diff --git a/src/opustags.h b/src/opustags.h
index 0639bb5..dbc3ab0 100644
--- a/src/opustags.h
+++ b/src/opustags.h
@@ -22,6 +22,8 @@ namespace ot {
  * The overflowing error family means that the end of packet was reached when attempting to read the
  * overflowing value. For example, overflowing_comment_count means that after reading the vendor
  * string, less than 4 bytes were left in the packet.
+ *
+ * When adding new status codes, make sure you update #error_message.
  */
 enum class status {
 	ok = 0,
@@ -47,6 +49,14 @@ enum class status {
 	sentinel,
 };
 
+/**
+ * Return an error message to show to user.
+ *
+ * For #ot::status::standard_error, the message is generated by strerror.
+ *
+ * The message is static, and must not be freed or modified. It is valid until the next call to
+ * #error_message, because of stderror.
+ */
 const char* error_message(status code);
 
 /**
diff --git a/t/error.cc b/t/error.cc
index 3b5e555..bf58ada 100644
--- a/t/error.cc
+++ b/t/error.cc
@@ -9,6 +9,24 @@ static void check_message()
 		throw failure("unexpected message for overflowing_comment_data");
 }
 
+static void check_errno()
+{
+	/* copy the messages in case strerror changes something */
+	std::string got, expected;
+
+	errno = EINVAL;
+	got = ot::error_message(ot::status::standard_error);
+	expected = strerror(errno);
+	if (got != expected)
+		throw failure("unexpected message for errno EINVAL");
+
+	errno = 0;
+	got = ot::error_message(ot::status::standard_error);
+	expected = strerror(errno);
+	if (got != expected)
+		throw failure("unexpected message for errno 0");
+}
+
 static void check_sentinel()
 {
 	if (ot::error_message(ot::status::sentinel) != nullptr)
@@ -20,8 +38,9 @@ static void check_sentinel()
 
 int main()
 {
-	std::cout << "1..2\n";
+	std::cout << "1..3\n";
 	run(check_message, "check a few error messages");
+	run(check_errno, "check the message for standard errors");
 	run(check_sentinel, "ensure the sentinel is respected");
 	return 0;
 }