diff --git a/include/common/buf.h b/include/common/buf.h
index 9647262..a1355e6 100644
--- a/include/common/buf.h
+++ b/include/common/buf.h
@@ -494,6 +494,9 @@
 {
 	size_t half = b_contig_space(b);
 
+	if (half > len)
+		half = len;
+
 	memcpy(b_tail(b), blk, half);
 
 	if (len > half)