diff --git a/lib/output.c b/lib/output.c
index 4373c30b2..004a70cf4 100644
--- a/lib/output.c
+++ b/lib/output.c
@@ -59,7 +59,7 @@ LWS_VISIBLE void lwsl_hexdump(void *vbuf, size_t len)
 		start = n;
 		p = line;
 
-		p += sprintf(p, "%04X: ", start);
+		p += sprintf(p, "%04zX: ", start);
 
 		for (m = 0; m < 16 && n < len; m++)
 			p += sprintf(p, "%02X ", buf[n++]);
diff --git a/test-server/test-ping.c b/test-server/test-ping.c
index de5672f7e..606ec604a 100644
--- a/test-server/test-ping.c
+++ b/test-server/test-ping.c
@@ -33,6 +33,7 @@
 #include <sys/ioctl.h>
 #include <poll.h>
 #include <unistd.h>
+#include <stddef.h>
 #endif
 
 #ifdef CMAKE_BUILD