diff --git a/include/sys/dsl_dir.h b/include/sys/dsl_dir.h
index 384f98e8f..f7c0d9acd 100644
--- a/include/sys/dsl_dir.h
+++ b/include/sys/dsl_dir.h
@@ -116,7 +116,7 @@ struct dsl_dir {
 	/* gross estimate of space used by in-flight tx's */
 	uint64_t dd_tempreserved[TXG_SIZE];
 	/* amount of space we expect to write; == amount of dirty data */
-	int64_t dd_space_towrite[TXG_SIZE];
+	uint64_t dd_space_towrite[TXG_SIZE];
 
 	dsl_deadlist_t dd_livelist;
 	bplist_t dd_pending_frees;
diff --git a/module/zfs/dsl_dir.c b/module/zfs/dsl_dir.c
index c1afaa6aa..18142cef9 100644
--- a/module/zfs/dsl_dir.c
+++ b/module/zfs/dsl_dir.c
@@ -1186,10 +1186,9 @@ dsl_dir_space_towrite(dsl_dir_t *dd)
 
 	ASSERT(MUTEX_HELD(&dd->dd_lock));
 
-	for (int i = 0; i < TXG_SIZE; i++) {
+	for (int i = 0; i < TXG_SIZE; i++)
 		space += dd->dd_space_towrite[i & TXG_MASK];
-		ASSERT3U(dd->dd_space_towrite[i & TXG_MASK], >=, 0);
-	}
+
 	return (space);
 }