diff --git a/mimic-iii/concepts/durations/arterial_line_durations.sql b/mimic-iii/concepts/durations/arterial_line_durations.sql
index 4d6231cf4..2f87ef307 100644
--- a/mimic-iii/concepts/durations/arterial_line_durations.sql
+++ b/mimic-iii/concepts/durations/arterial_line_durations.sql
@@ -131,7 +131,7 @@ with mv as
     , charttime_lag
     -- if the current observation indicates a line is present
     -- calculate the time since the last charted line
-    , charttime - charttime_lag as arterial_line_duration
+    , DATETIME_DIFF(charttime, charttime_lag, HOUR) as arterial_line_duration
     -- now we determine if the current line is "new"
     -- new == no documentation for 16 hours
     , case