diff --git a/lib/iris/fileformats/pp_load_rules.py b/lib/iris/fileformats/pp_load_rules.py
index c0a4081970..b6aacb382f 100644
--- a/lib/iris/fileformats/pp_load_rules.py
+++ b/lib/iris/fileformats/pp_load_rules.py
@@ -627,7 +627,7 @@ def _convert_time_coords(
     def date2hours(t):
         epoch_hours = _epoch_date_hours(epoch_hours_unit, t)
         if t.minute == 0 and t.second == 0:
-            epoch_hours = round(epoch_hours)
+            epoch_hours = np.around(epoch_hours)
         return epoch_hours
 
     def date2year(t_in):
diff --git a/requirements/core.txt b/requirements/core.txt
index 3f2f458595..9d0d6526dd 100644
--- a/requirements/core.txt
+++ b/requirements/core.txt
@@ -8,7 +8,7 @@ cartopy>=0.12
 cf-units>=2
 cftime==1.1.3
 dask[array]>=2  #conda: dask>=2
-matplotlib
+matplotlib<3.3
 netcdf4
 numpy>=1.14
 scipy