--- b/tests/sys/fs/fusefs/io.cc	
+++ b/tests/sys/fs/fusefs/io.cc	
@@ -194,6 +194,26 @@ void SetUp()
 		}, Eq(true)),
 		_)
 	).WillRepeatedly(Invoke(ReturnErrno(0)));
+	EXPECT_CALL(*m_mock, process(
+		ResultOf([=](auto in) {
+			return (in.header.opcode == FUSE_FALLOCATE &&
+				in.header.nodeid == ino &&
+				in.body.fallocate.mode ==
+					(FUSE_FALLOC_FL_KEEP_SIZE |
+					 FUSE_FALLOC_FL_PUNCH_HOLE));
+
+		}, Eq(true)),
+		_)
+	).WillRepeatedly(Invoke(ReturnImmediate([=](auto in, auto& out) {
+		spacectl_range rqsr = {
+			.r_offset = (off_t)in.body.fallocate.offset,
+			.r_len = (off_t)in.body.fallocate.length
+		};
+		ASSERT_EQ(0, fspacectl(m_backing_fd, SPACECTL_DEALLOC, &rqsr,
+					0, &rqsr))
+			<< strerror(errno);
+		out.header.len = sizeof(out.header);
+	})));
 
 	m_test_fd = open(FULLPATH, O_RDWR );
 	EXPECT_LE(0, m_test_fd) << strerror(errno);
@@ -222,6 +242,24 @@ void do_closeopen()
 	ASSERT_LE(0, m_control_fd) << strerror(errno);
 }
 
+void do_fspacectl(ssize_t size, off_t offs)
+{
+	struct spacectl_range rqsr = {
+		.r_offset = offs,
+		.r_len = size,
+	};
+	struct spacectl_range rmsr;
+
+	ASSERT_EQ(0, fspacectl(m_test_fd, SPACECTL_DEALLOC, &rqsr, 0, &rmsr))
+		<< strerror(errno);
+	EXPECT_EQ(0, rmsr.r_len);
+	EXPECT_EQ(offs + size, rmsr.r_offset);
+	ASSERT_EQ(0, fspacectl(m_control_fd, SPACECTL_DEALLOC, &rqsr, 0, &rmsr))
+		<< strerror(errno);
+	EXPECT_EQ(0, rmsr.r_len);
+	EXPECT_EQ(offs + size, rmsr.r_offset);
+}
+
 void do_ftruncate(off_t offs)
 {
 	ASSERT_EQ(0, ftruncate(m_test_fd, offs)) << strerror(errno);
@@ -506,6 +544,27 @@ TEST_P(Io, resize_a_valid_buffer_while_extending)
 	close(m_test_fd);
 }
 
+/* Revealed with bfffs 4a0eef6c6011fa3c0ab898dbd647c1ea27986004 using fsx c3e726d6de39d4b2641cd8b49bbd19beef456604
+ *
+ * fsx -f fsx.toml -N 1000 -P /tmp -S 2153242284826767701 /testpool/tmp/fsx.bin
+ *
+ * fsx.toml:
+ * nomsyncafterwrite = true
+ * [weights]
+ * close_open = 0.1
+ * invalidate = 0.2
+ * truncate = 1
+ * fsync = 1
+ * fdatasync = 1
+ * punch_hole = 100
+ */
+TEST_P(IoCacheable, fsx_bfffs_fspacectl)
+{
+	do_mapwrite(0x80f1, 0x1ffb4);
+	do_fspacectl(0x1f7, 0x27eae);
+	do_mapread(0xb982, 0x16252);
+}
+
 INSTANTIATE_TEST_CASE_P(Io, Io,
 	Combine(Bool(),					/* async read */
 		Values(0x1000, 0x10000, 0x20000),	/* m_maxwrite */