diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
index 0c943e8f976f..c19c6e21e968 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
@@ -5140,7 +5140,7 @@ static boolean_t
 arc_is_overflowing(void)
 {
 	/* Always allow at least one block of overflow */
-	uint64_t overflow = MAX(SPA_MAXBLOCKSIZE,
+	int64_t overflow = MAX(SPA_MAXBLOCKSIZE,
 	    arc_c >> zfs_arc_overflow_shift);
 
 	/*
@@ -5152,7 +5152,7 @@ arc_is_overflowing(void)
 	 * in the ARC. In practice, that's in the tens of MB, which is low
 	 * enough to be safe.
 	 */
-	return (aggsum_lower_bound(&arc_size) >= arc_c + overflow);
+	return (aggsum_lower_bound(&arc_size) >= (int64_t)arc_c + overflow);
 }
 
 static abd_t *