diff --git a/src/buffer.c b/src/buffer.c
index 47b40ce2..9e6c1126 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -173,7 +173,7 @@ bufputs(struct buf *buf, const char *str)
 
 /* bufputc: appends a single uint8_t to a buffer */
 void
-bufputc(struct buf *buf, int c)
+bufputc(struct buf *buf, uint8_t c)
 {
 	assert(buf && buf->unit);
 
diff --git a/src/buffer.h b/src/buffer.h
index 221d142e..7235567e 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -75,7 +75,7 @@ void bufput(struct buf *, const void *, size_t);
 void bufputs(struct buf *, const char *);
 
 /* bufputc: appends a single char to a buffer */
-void bufputc(struct buf *, int);
+void bufputc(struct buf *, uint8_t);
 
 /* bufrelease: decrease the reference count and free the buffer if needed */
 void bufrelease(struct buf *);