diff --git a/tests/Makefile.am b/tests/Makefile.am
index ab46af1..ff3175d 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -326,7 +326,6 @@
 	     ksysent.sed \
 	     lstatx.c \
 	     memfd_create.expected \
-	     mmsg.expected \
 	     mq.expected \
 	     net.expected \
 	     net-fd.expected \
diff --git a/tests/mmsg.c b/tests/mmsg.c
index ba7fc3e..fa1ee8b 100644
--- a/tests/mmsg.c
+++ b/tests/mmsg.c
@@ -34,15 +34,20 @@
 
 # include <assert.h>
 # include <errno.h>
+# include <stdio.h>
 # include <unistd.h>
 # include <sys/socket.h>
 
-#ifndef HAVE_STRUCT_MMSGHDR
+# ifndef HAVE_STRUCT_MMSGHDR
 struct mmsghdr {
 	struct msghdr msg_hdr;
 	unsigned msg_len;
 };
-#endif
+# endif
+
+# define LENGTH_OF(arg) ((unsigned int) sizeof(arg) - 1)
+
+static FILE *logfp;
 
 static int
 send_mmsg(int fd, struct mmsghdr *vec, unsigned int vlen, unsigned int flags)
@@ -53,6 +58,9 @@
 		     (unsigned long) flags);
 	if (rc >= 0 || ENOSYS != errno)
 		return rc;
+	fprintf(logfp,
+		"sendmmsg(%d, %p, %u, MSG_DONTROUTE|MSG_NOSIGNAL)"
+		" = -1 ENOSYS (%m)\n", fd, vec, vlen);
 #endif
 #ifdef HAVE_SENDMMSG
 	rc = sendmmsg(fd, vec, vlen, flags);
@@ -70,6 +78,9 @@
 		     (unsigned long) flags, timeout);
 	if (rc >= 0 || ENOSYS != errno)
 		return rc;
+	fprintf(logfp,
+		"recvmmsg(%d, %p, %u, MSG_DONTWAIT, NULL)"
+		" = -1 ENOSYS (%m)\n", fd, vec, vlen);
 #endif
 #ifdef HAVE_RECVMMSG
 	rc = recvmmsg(fd, vec, vlen, flags, timeout);
@@ -83,6 +94,10 @@
 	const int R = 0, W = 1;
 	int sv[2];
 
+	int logfd = dup(1);
+	assert(logfd > 2);
+	assert((logfp = fdopen(logfd, "w")));
+
 	(void) close(0);
 	(void) close(1);
 	if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sv))
@@ -93,20 +108,24 @@
 	static const char one[] = "one";
 	static const char two[] = "two";
 	static const char three[] = "three";
-	void *copy_one = tail_memdup(one, sizeof(one) - 1);
-	void *copy_two = tail_memdup(two, sizeof(two) - 1);
-	void *copy_three = tail_memdup(three, sizeof(three) - 1);
+	static const char ascii_one[] = "6f 6e 65";
+	static const char ascii_two[] = "74 77 6f";
+	static const char ascii_three[] = "74 68 72 65 65";
+
+	void *copy_one = tail_memdup(one, LENGTH_OF(one));
+	void *copy_two = tail_memdup(two, LENGTH_OF(two));
+	void *copy_three = tail_memdup(three, LENGTH_OF(three));
 
 	struct iovec iov[] = {
 		{
 			.iov_base = copy_one,
-			.iov_len = sizeof(one) - 1
+			.iov_len = LENGTH_OF(one)
 		}, {
 			.iov_base = copy_two,
-			.iov_len = sizeof(two) - 1
+			.iov_len = LENGTH_OF(two)
 		}, {
 			.iov_base = copy_three,
-			.iov_len = sizeof(three) - 1
+			.iov_len = LENGTH_OF(three)
 		}
 	};
 	struct iovec *copy_iov = tail_memdup(iov, sizeof(iov));
@@ -125,17 +144,60 @@
 		}
 	};
 	void *copy_mmh = tail_memdup(mmh, sizeof(mmh));
-# define n_mmh (sizeof(mmh)/sizeof(mmh[0]))
+# define n_mmh ((unsigned int) (sizeof(mmh)/sizeof(mmh[0])))
 
 	int r = send_mmsg(W, copy_mmh, n_mmh, MSG_DONTROUTE | MSG_NOSIGNAL);
 	if (r < 0 && errno == ENOSYS)
 		perror_msg_and_skip("sendmmsg");
-	assert((size_t)r == n_mmh);
+	assert(r == (int) n_mmh);
 	assert(close(W) == 0);
+	fprintf(logfp,
+		"sendmmsg(%d, {{{msg_name(0)=NULL, msg_iov(%u)=[{\"%s\", %u}"
+		", {\"%s\", %u}], msg_controllen=0, msg_flags=0}, %u}"
+		", {{msg_name(0)=NULL, msg_iov(%u)=[{\"%s\", %u}]"
+		", msg_controllen=0, msg_flags=0}, %u}}, %u"
+		", MSG_DONTROUTE|MSG_NOSIGNAL) = %d\n"
+		" = %u buffers in vector 0\n"
+		" * %u bytes in buffer 0\n"
+		" | 00000  %-48s  %-16s |\n"
+		" * %u bytes in buffer 1\n"
+		" | 00000  %-48s  %-16s |\n"
+		" = %u buffers in vector 1\n"
+		" * %u bytes in buffer 0\n"
+		" | 00000  %-48s  %-16s |\n",
+		W, 2, one, LENGTH_OF(one), two, LENGTH_OF(two),
+		LENGTH_OF(one) +  LENGTH_OF(two),
+		1, three, LENGTH_OF(three), LENGTH_OF(three),
+		n_mmh, r,
+		2, LENGTH_OF(one), ascii_one, one,
+		LENGTH_OF(two), ascii_two, two,
+		1, LENGTH_OF(three), ascii_three, three);
 
-	assert(recv_mmsg(R, copy_mmh, n_mmh, MSG_DONTWAIT, NULL) == n_mmh);
+	assert(recv_mmsg(R, copy_mmh, n_mmh, MSG_DONTWAIT, NULL) == (int) n_mmh);
 	assert(close(R) == 0);
+	fprintf(logfp,
+		"recvmmsg(%d, {{{msg_name(0)=NULL, msg_iov(%u)=[{\"%s\", %u}"
+		", {\"%s\", %u}], msg_controllen=0, msg_flags=0}, %u}"
+		", {{msg_name(0)=NULL, msg_iov(%u)=[{\"%s\", %u}]"
+		", msg_controllen=0, msg_flags=0}, %u}}, %u"
+		", MSG_DONTWAIT, NULL) = %d (left NULL)\n"
+		" = %u buffers in vector 0\n"
+		" * %u bytes in buffer 0\n"
+		" | 00000  %-48s  %-16s |\n"
+		" * %u bytes in buffer 1\n"
+		" | 00000  %-48s  %-16s |\n"
+		" = %u buffers in vector 1\n"
+		" * %u bytes in buffer 0\n"
+		" | 00000  %-48s  %-16s |\n",
+		R, 2, one, LENGTH_OF(one), two, LENGTH_OF(two),
+		LENGTH_OF(one) +  LENGTH_OF(two),
+		1, three, LENGTH_OF(three), LENGTH_OF(three),
+		n_mmh, r,
+		2, LENGTH_OF(one), ascii_one, one,
+		LENGTH_OF(two), ascii_two, two,
+		1, LENGTH_OF(three), ascii_three, three);
 
+	fprintf(logfp, "+++ exited with 0 +++\n");
 	return 0;
 }
 
diff --git a/tests/mmsg.expected b/tests/mmsg.expected
deleted file mode 100644
index 708e029..0000000
--- a/tests/mmsg.expected
+++ /dev/null
@@ -1,19 +0,0 @@
-sendmmsg(1, {{{msg_name(0)=NULL, msg_iov(2)=[{"one", 3}, {"two", 3}], msg_controllen=0, msg_flags=0}, 6}, {{msg_name(0)=NULL, msg_iov(1)=[{"three", 5}], msg_controllen=0, msg_flags=0}, 5}}, 2, MSG_DONTROUTE|MSG_NOSIGNAL) = 2
- = 2 buffers in vector 0
- * 3 bytes in buffer 0
- | 00000  6f 6e 65                                          one              |
- * 3 bytes in buffer 1
- | 00000  74 77 6f                                          two              |
- = 1 buffers in vector 1
- * 5 bytes in buffer 0
- | 00000  74 68 72 65 65                                    three            |
-recvmmsg(0, {{{msg_name(0)=NULL, msg_iov(2)=[{"one", 3}, {"two", 3}], msg_controllen=0, msg_flags=0}, 6}, {{msg_name(0)=NULL, msg_iov(1)=[{"three", 5}], msg_controllen=0, msg_flags=0}, 5}}, 2, MSG_DONTWAIT, NULL) = 2 (left NULL)
- = 2 buffers in vector 0
- * 3 bytes in buffer 0
- | 00000  6f 6e 65                                          one              |
- * 3 bytes in buffer 1
- | 00000  74 77 6f                                          two              |
- = 1 buffers in vector 1
- * 5 bytes in buffer 0
- | 00000  74 68 72 65 65                                    three            |
-+++ exited with 0 +++
diff --git a/tests/mmsg.test b/tests/mmsg.test
index 0237df8..073340f 100755
--- a/tests/mmsg.test
+++ b/tests/mmsg.test
@@ -4,8 +4,10 @@
 
 . "${srcdir=.}/init.sh"
 
-run_prog
-run_strace -e trace=recvmmsg,sendmmsg -e read=0 -e write=1 $args
-match_diff
+run_prog > /dev/null
+OUT="$LOG.out"
+run_strace -e trace=recvmmsg,sendmmsg -e read=0 -e write=1 $args > "$OUT"
+match_diff "$LOG" "$OUT"
+rm -f "$OUT"
 
 exit 0