diff --git a/ccan/ccan/mem/mem.c b/ccan/ccan/mem/mem.c
index 13027a2a7..fcd4dda9f 100644
--- a/ccan/ccan/mem/mem.c
+++ b/ccan/ccan/mem/mem.c
@@ -123,6 +123,6 @@ void memtaint(void *data, size_t len)
 	memcpy(p, tainter, len);
 
 #if HAVE_VALGRIND_MEMCHECK_H
-	VALGRIND_MAKE_MEM_UNDEFINED(data, len);
+	(void)VALGRIND_MAKE_MEM_UNDEFINED(data, len);
 #endif
 }
diff --git a/ccan/ccan/mem/mem.h b/ccan/ccan/mem/mem.h
index 20286dcbe..617925757 100644
--- a/ccan/ccan/mem/mem.h
+++ b/ccan/ccan/mem/mem.h
@@ -244,7 +244,7 @@ void memswap(void *a, void *b, size_t n);
 #include <valgrind/memcheck.h>
 static inline void *memcheck_(const void *data, size_t len)
 {
-	VALGRIND_CHECK_MEM_IS_DEFINED(data, len);
+	(void)VALGRIND_CHECK_MEM_IS_DEFINED(data, len);
 	return (void *)data;
 }
 #else