diff --git a/src/misc.c b/src/misc.c
index c3b702d..c98603b 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -188,7 +188,7 @@ void _libssh2_debug(LIBSSH2_SESSION *session, int context, const char *format, .
 	len = snprintf(buffer, 1535, "[libssh2] %s: ", contexts[context]);
 
 	va_start(vargs, format);
-	len += vsnprintf(buffer, 1535 - len, format, vargs);
+	len += vsnprintf(buffer + len, 1535 - len, format, vargs);
 	buffer[len] = '\n';
 	va_end(vargs);
 	write(2, buffer, len + 1);