diff --git a/module/zfs/include/sys/zfs_debug.h b/module/zfs/include/sys/zfs_debug.h
index 3f3d8125e8..f08d7cd2bc 100644
--- a/module/zfs/include/sys/zfs_debug.h
+++ b/module/zfs/include/sys/zfs_debug.h
@@ -55,8 +55,16 @@ extern int zfs_flags;
 
 #ifdef ZFS_DEBUG
 #if defined(_KERNEL) && defined(HAVE_SPL)
-#include <sys/debug.h>
-#define dprintf(...) CDEBUG_LIMIT(D_DPRINTF, __VA_ARGS__)
+/*
+ * Log ZFS debug messages as the spl SS_USER1 subsystem.
+ */
+#include <spl-debug.h>
+
+#ifdef SS_DEBUG_SUBSYS
+#undef SS_DEBUG_SUBSYS
+#endif
+#define SS_DEBUG_SUBSYS SS_USER1
+#define dprintf(...) SDEBUG_LIMIT(SD_DPRINTF, __VA_ARGS__)
 #else
 extern void __dprintf(const char *file, const char *func,
     int line, const char *fmt, ...);
diff --git a/module/zfs/vdev_disk.c b/module/zfs/vdev_disk.c
index 799587a809..dbf9b08e76 100644
--- a/module/zfs/vdev_disk.c
+++ b/module/zfs/vdev_disk.c
@@ -235,15 +235,13 @@ BIO_END_IO_PROTO(vdev_disk_physio_completion, bio, size, error)
 	int rc;
 
 	/* Fatal error but print some useful debugging before asserting */
-	if (dr == NULL) {
-		printk("FATAL: bio->bi_private == NULL\n"
-		       "bi_next: %p, bi_flags: %lx, bi_rw: %lu, bi_vcnt: %d\n"
-		       "bi_idx: %d, bi_size: %d, bi_end_io: %p, bi_cnt: %d\n",
-		       bio->bi_next, bio->bi_flags, bio->bi_rw, bio->bi_vcnt,
-		       bio->bi_idx, bio->bi_size, bio->bi_end_io,
-		       atomic_read(&bio->bi_cnt));
-		SBUG();
-	}
+	if (dr == NULL)
+		PANIC("dr == NULL, bio->bi_private == NULL\n"
+		    "bi_next: %p, bi_flags: %lx, bi_rw: %lu, bi_vcnt: %d\n"
+		    "bi_idx: %d, bi_size: %d, bi_end_io: %p, bi_cnt: %d\n",
+		    bio->bi_next, bio->bi_flags, bio->bi_rw, bio->bi_vcnt,
+		    bio->bi_idx, bio->bi_size, bio->bi_end_io,
+		    atomic_read(&bio->bi_cnt));
 
 #ifndef HAVE_2ARGS_BIO_END_IO_T
 	if (bio->bi_size)