2 files changed, 10 insertions, 2 deletions
diff --git a/src/cbuf.c b/src/cbuf.c
index e519578..372cc97 100644
--- a/src/cbuf.c
+++ b/src/cbuf.c
@@ -143,13 +143,13 @@ cbuf_write(struct cbuf *cbuf, size_t index, const void *buf, size_t size)
     uint8_t *start, *end, *buf_end;
     size_t new_end, skip;
 
-    if (!cbuf_index_valid(cbuf, index)) {
+    if (!cbuf_range_valid(cbuf, index, cbuf->end)) {
         return EINVAL;
     }
 
     new_end = index + size;
 
-    if (!cbuf_index_valid(cbuf, new_end)) {
+    if (!cbuf_range_valid(cbuf, cbuf->start, new_end)) {
         cbuf->end = new_end;
         cbuf_update_start(cbuf);
 
diff --git a/src/cbuf.h b/src/cbuf.h
index 9175bb4..437064e 100644
--- a/src/cbuf.h
+++ b/src/cbuf.h
@@ -89,6 +89,14 @@ cbuf_index_valid(const struct cbuf *cbuf, size_t index)
            && ((cbuf->end - index) <= cbuf_size(cbuf));
 }
 
+static inline bool
+cbuf_range_valid(const struct cbuf *cbuf, size_t start, size_t end)
+{
+    return (((end - start) <= cbuf_size(cbuf))
+            && ((start - cbuf->start) <= cbuf_size(cbuf))
+            && ((cbuf->end - end) <= cbuf_size(cbuf)));
+}
+
 /*
  * Initialize a circular buffer.
  *