diff --git a/src/modules/module-protocol-pulse/message.c b/src/modules/module-protocol-pulse/message.c
index 1ad3d6a76..91413070d 100644
--- a/src/modules/module-protocol-pulse/message.c
+++ b/src/modules/module-protocol-pulse/message.c
@@ -181,7 +181,10 @@ static int read_arbitrary(struct message *m, const void **val, size_t *length)
 
 static int read_string(struct message *m, char **str)
 {
-	uint32_t n, maxlen = m->length - m->offset;
+	uint32_t n, maxlen;
+	if (m->offset + 1 > m->length)
+		return -ENOSPC;
+	maxlen = m->length - m->offset;
 	n = strnlen(SPA_PTROFF(m->data, m->offset, char), maxlen);
 	if (n == maxlen)
 		return -EINVAL;