diff --git a/src/buffer.hpp b/src/buffer.hpp
index 082d584e2cf58f96eec83ac060d53225042168aa..d4a911fc211016fe5e4c7af64a2b2e4328cd26fc 100644
--- a/src/buffer.hpp
+++ b/src/buffer.hpp
@@ -27,11 +27,13 @@ Buf *buf_sprintf(const char *format, ...)
 Buf *buf_vprintf(const char *format, va_list ap);
 
 static inline size_t buf_len(Buf *buf) {
+    assert(buf);
     assert(buf->list.length);
     return buf->list.length - 1;
 }
 
 static inline char *buf_ptr(Buf *buf) {
+    assert(buf);
     assert(buf->list.length);
     return buf->list.items;
 }