diff --git a/tests/sys/fs/fusefs/bmap.cc b/tests/sys/fs/fusefs/bmap.cc
--- a/tests/sys/fs/fusefs/bmap.cc
+++ b/tests/sys/fs/fusefs/bmap.cc
@@ -83,10 +83,14 @@
 TEST_F(Bmap, bmap)
 {
 	struct fiobmap2_arg arg;
-	const off_t filesize = 1 << 20;
-	const ino_t ino = 42;
-	int64_t lbn = 10;
+	/*
+	 * Pick fsize and lbn large enough that max length runs won't reach
+	 * either beginning or end of file
+	 */
+	const off_t filesize = 1 << 30;
+	int64_t lbn = 100;
 	int64_t pbn = 12345;
+	const ino_t ino = 42;
 	int fd;
 
 	expect_lookup(RELPATH, 42, filesize);
@@ -112,7 +116,7 @@
 TEST_F(Bmap, default_)
 {
 	struct fiobmap2_arg arg;
-	const off_t filesize = 1 << 20;
+	const off_t filesize = 1 << 30;
 	const ino_t ino = 42;
 	int64_t lbn;
 	int fd;
diff --git a/tests/sys/fs/fusefs/mockfs.hh b/tests/sys/fs/fusefs/mockfs.hh
--- a/tests/sys/fs/fusefs/mockfs.hh
+++ b/tests/sys/fs/fusefs/mockfs.hh
@@ -72,6 +72,14 @@
 
 extern int verbosity;
 
+/*
+ * The maximum that a test case can set max_write, limited by the buffer
+ * supplied when reading from /dev/fuse.  This limitation is imposed by
+ * fusefs-libs, but not by the FUSE protocol.
+ */
+const uint32_t max_max_write = 0x20000;
+
+
 /* This struct isn't defined by fuse_kernel.h or libfuse, but it should be */
 struct fuse_create_out {
 	struct fuse_entry_out	entry;
@@ -138,8 +146,17 @@
 union fuse_payloads_in {
 	fuse_access_in	access;
 	fuse_bmap_in	bmap;
-	/* value is from fuse_kern_chan.c in fusefs-libs */
-	uint8_t		bytes[0x21000 - sizeof(struct fuse_in_header)];
+	/*
+	 * In fusefs-libs 3.4.2 and below the buffer size is fixed at 0x21000
+	 * minus the header sizes.  fusefs-libs 3.4.3 (and FUSE Protocol 7.29)
+	 * add a FUSE_MAX_PAGES option that allows it to be greater.
+	 *
+	 * See fuse_kern_chan.c in fusefs-libs 2.9.9 and below, or
+	 * FUSE_DEFAULT_MAX_PAGES_PER_REQ in fusefs-libs 3.4.3 and above.
+	 */
+	uint8_t		bytes[
+	    max_max_write + 0x1000 - sizeof(struct fuse_in_header)
+	];
 	fuse_create_in	create;
 	fuse_flush_in	flush;
 	fuse_fsync_in	fsync;
diff --git a/tests/sys/fs/fusefs/mockfs.cc b/tests/sys/fs/fusefs/mockfs.cc
--- a/tests/sys/fs/fusefs/mockfs.cc
+++ b/tests/sys/fs/fusefs/mockfs.cc
@@ -365,7 +365,7 @@
 	m_daemon_id = NULL;
 	m_kernel_minor_version = kernel_minor_version;
 	m_maxreadahead = max_readahead;
-	m_maxwrite = max_write;
+	m_maxwrite = MIN(max_write, max_max_write);
 	m_nready = -1;
 	m_pm = pm;
 	m_time_gran = time_gran;
diff --git a/tests/sys/fs/fusefs/utils.hh b/tests/sys/fs/fusefs/utils.hh
--- a/tests/sys/fs/fusefs/utils.hh
+++ b/tests/sys/fs/fusefs/utils.hh
@@ -55,7 +55,6 @@
 bool is_unsafe_aio_enabled(void);
 
 extern const uint32_t libfuse_max_write;
-extern const uint32_t default_max_write;
 class FuseTest : public ::testing::Test {
 	protected:
 	uint32_t m_maxreadahead;
@@ -80,7 +79,7 @@
 
 	FuseTest():
 		m_maxreadahead(0),
-		m_maxwrite(default_max_write),
+		m_maxwrite(0),
 		m_init_flags(0),
 		m_allow_other(false),
 		m_default_permissions(false),
diff --git a/tests/sys/fs/fusefs/utils.cc b/tests/sys/fs/fusefs/utils.cc
--- a/tests/sys/fs/fusefs/utils.cc
+++ b/tests/sys/fs/fusefs/utils.cc
@@ -59,13 +59,6 @@
  */
 const uint32_t libfuse_max_write = 32 * getpagesize() + 0x1000 - 4096;
 
-/* 
- * Set the default max_write to a distinct value from MAXPHYS to catch bugs
- * that confuse the two.
- */
-const uint32_t default_max_write = MIN(libfuse_max_write, MAXPHYS / 2);
-
-
 /* Check that fusefs(4) is accessible and the current user can mount(2) */
 void check_environment()
 {
@@ -156,6 +149,12 @@
 	ASSERT_EQ(0, sysctlbyname(maxphys_node, &val, &size, NULL, 0))
 		<< strerror(errno);
 	m_maxphys = val;
+	/*
+	 * Set the default max_write to a distinct value from MAXPHYS to catch
+	 * bugs that confuse the two.
+	 */
+	if (m_maxwrite == 0)
+		m_maxwrite = MIN(libfuse_max_write, (uint32_t)m_maxphys / 2);
 
 	try {
 		m_mock = new MockFS(m_maxreadahead, m_allow_other,
diff --git a/tests/sys/fs/fusefs/write.cc b/tests/sys/fs/fusefs/write.cc
--- a/tests/sys/fs/fusefs/write.cc
+++ b/tests/sys/fs/fusefs/write.cc
@@ -166,6 +166,7 @@
 public:
 virtual void SetUp() {
 	m_async = true;
+	m_maxwrite = 65536;
 	WriteBack::SetUp();
 }
 };
@@ -194,6 +195,19 @@
 }
 };
 
+/* Tests relating to the server's max_write property */
+class WriteMaxWrite: public Write {
+public:
+virtual void SetUp() {
+	/*
+	 * For this test, m_maxwrite must be less than either m_maxbcachebuf or
+	 * maxphys.
+	 */
+	m_maxwrite = 32768;
+	Write::SetUp();
+}
+};
+
 void sigxfsz_handler(int __unused sig) {
 	Write::s_sigxfsz = 1;
 }
@@ -643,7 +657,7 @@
 }
 
 /* fuse(4) should not issue writes of greater size than the daemon requests */
-TEST_F(Write, write_large)
+TEST_F(WriteMaxWrite, write)
 {
 	const char FULLPATH[] = "mountpoint/some_file.txt";
 	const char RELPATH[] = "some_file.txt";
@@ -653,6 +667,8 @@
 	ssize_t halfbufsize, bufsize;
 
 	halfbufsize = m_mock->m_maxwrite;
+	if (halfbufsize >= m_maxbcachebuf || halfbufsize >= m_maxphys)
+		GTEST_SKIP() << "Must lower m_maxwrite for this test";
 	bufsize = halfbufsize * 2;
 	contents = (int*)malloc(bufsize);
 	ASSERT_NE(nullptr, contents);