diff --git a/src/ILAMB/Variable.py b/src/ILAMB/Variable.py
index 1ec31b5..0d763f2 100644
--- a/src/ILAMB/Variable.py
+++ b/src/ILAMB/Variable.py
@@ -167,6 +167,7 @@ def __init__(self, **keywords):
 
         # Add handling for some units which cf_units does not support
         unit = unit.replace("psu", "1e-3")
+        unit = unit.replace("proportion", "1")
 
         if not np.ma.isMaskedArray(data):
             data = np.ma.masked_array(data)
@@ -1539,9 +1540,20 @@ def interpolate(
                 data = data.data[ind]
                 data = np.ma.masked_array(data, mask=mask)
                 if self.data_bnds is not None:
-                    args.append([0, 1])
-                    ind = np.ix_(*args)
-                    data_bnds = self.data_bnds[ind]
+
+                    if self.data_bnds.shape == self.data.shape:
+                        ind = np.ix_(*args)
+                        # one std?
+                        data_bnds = np.ma.stack(
+                                            [self.data[ind]-self.data_bnds[ind],
+                                             self.data[ind]+self.data_bnds[ind]], axis=len(args))
+
+                        self.data_bnds = data_bnds
+                    else:
+                        args.append([0, 1])
+                        ind = np.ix_(*args)
+                        data_bnds = self.data_bnds[ind]
+
                 np.seterr(under="ignore", over="ignore")
                 frac = self.area / il.CellAreas(
                     self.lat, self.lon, self.lat_bnds, self.lon_bnds