diff --git a/src/@dseries/firstobservedperiod.m b/src/@dseries/firstobservedperiod.m
index 0ba14448c11e9afde932ba0c5751174852c552ec..13b8b95973c21c8cb0e8ce562f80d05a9a575cd1 100644
--- a/src/@dseries/firstobservedperiod.m
+++ b/src/@dseries/firstobservedperiod.m
@@ -26,7 +26,7 @@ function d = firstobservedperiod(o) % --*-- Unitary tests --*--
 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
 
 b = ~isnan(o);
-c = find(prod(b, 2));
+c = find(prod(double(b), 2));
 
 if isempty(c)
     error('No overlapping non-NaN data points found in dseries.');
diff --git a/src/@dseries/lastobservedperiod.m b/src/@dseries/lastobservedperiod.m
index a9d1b99fbf6c3f05c1daef12f32778fc860d35fb..2863e87baf450e81405418fe26e2324d11f8dfff 100644
--- a/src/@dseries/lastobservedperiod.m
+++ b/src/@dseries/lastobservedperiod.m
@@ -26,7 +26,7 @@ function d = lastobservedperiod(o) % --*-- Unitary tests --*--
 % along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
 
 b = ~isnan(o);
-c = find(prod(b, 2));
+c = find(prod(double(b), 2));
 if isempty(c)
     error('No overlapping non-NaN data points found in dseries.');
 end