diff --git a/src/Clock.cpp b/src/Clock.cpp
index 529012f..d2827c2 100644
--- a/src/Clock.cpp
+++ b/src/Clock.cpp
@@ -45,7 +45,20 @@
 }
 
 const char *clock_iso8601string(struct timeval time) {
-	return clock_timestring(time, "%Y-%m-%dT%H:%M:%S");
+	const char *timestring = clock_timestring(time, "%Y-%m-%dT%H:%M:%S");
+
+	static char buffer[128];
+	int buffer_size = sizeof(buffer);
+	int written;
+	written = snprintf(
+		buffer, buffer_size, "%s.%06li", timestring, time.tv_usec);
+
+	if (written >= buffer_size) {
+		// It overflowed, so return something useful
+		return "(iso8601 overflow)";
+	} else {
+		return buffer;
+	}
 }
 
 const char *clock_iso8601string_now(void) {