+	/* Closing the device causes the buffer to be reset. */
+	for (size_t i = 0; i < len; i++) {
+		ATF_REQUIRE_MSG(buf[i] == 0 || buf[i] == 0xa5,
+		    "mmap data corrupted at offset %zu: got 0x%02x", i, buf[i]);
+	}
+	memset(buf, 0xa5, len);
+
+	ATF_REQUIRE(munmap(buf, len) == 0);
+}
+
 ATF_TP_ADD_TCS(tp)
 {
 	ATF_TP_ADD_TC(tp, mmap_offset_overflow);
+	ATF_TP_ADD_TC(tp, mmap_buffer_lifetime);
 
 	return (atf_no_error());
 }