diff --git a/pycrate_asn1rt/setobj.py b/pycrate_asn1rt/setobj.py
index fcb33e0..b3f3eab 100644
--- a/pycrate_asn1rt/setobj.py
+++ b/pycrate_asn1rt/setobj.py
@@ -851,7 +851,7 @@ def is_empty(self):
         return self._rv == [] and self._rr == []
     
     def is_ext(self):
-        return self._er is not None
+        return self._ev is not None
     
     def __contains__(self, v):
         if self._CONTAIN_WEXT:
@@ -928,13 +928,14 @@ def intersect(self, S):
                 if not ret.in_root(v) and not ret.in_ext(v):
                     ret._ev.append(v)
             # 4.3) add self and S root values not intersecting
-            for v in self.root:
+            # (root ranges are already part of ret._er, from 4.1)
+            for v in self._rv:
                 if not ret.in_root(v) and not ret.in_ext(v):
                     ret._ev.append(v)
-            for v in S.root:
+            for v in S._rv:
                 if not ret.in_root(v) and not ret.in_ext(v):
                     ret._ev.append(v)
-        ret._init()
+        ret._init(True, True)
         return ret
     
     def get_root_dyn(self):
diff --git a/test/test_asn1rt.py b/test/test_asn1rt.py
index 9680d40..e556c5d 100644
--- a/test/test_asn1rt.py
+++ b/test/test_asn1rt.py
@@ -2157,6 +2157,24 @@ def _test_rt_base():
     
     return 0
 
+def test_setobj_intersect():
+    # integer root ranges, for non-extensible and extensible sets
+    for ev in (None, []):
+        left  = ASN1Set(rr=[ASN1RangeInt(0, 10)], ev=ev)
+        right = ASN1Set(rr=[ASN1RangeInt(5, 15)], ev=ev)
+        inter = left.intersect(right)
+        assert( [(r.lb, r.ub) for r in inter._rr] == [(5, 10)] )
+        assert( inter.in_root(5) and inter.in_root(10) )
+        assert( not inter.in_root(4) and not inter.in_root(11) )
+        assert( inter.is_ext() == (ev is not None) )
+    # individual root values outside the intersection go to the extension
+    left  = ASN1Set(rv=[20], rr=[ASN1RangeInt(0, 10)], ev=[])
+    right = ASN1Set(rr=[ASN1RangeInt(5, 15)], ev=[])
+    inter = left.intersect(right)
+    assert( inter.in_root(7) and not inter.in_root(20) )
+    assert( inter.in_ext(20) )
+    return 0
+
 def test_rt_base():
     _load_rt_base()
     _test_rt_base()
diff --git a/test/test_pycrate.py b/test/test_pycrate.py
index 1fd222b..10b44b2 100644
--- a/test/test_pycrate.py
+++ b/test/test_pycrate.py
@@ -237,6 +237,7 @@ def test_asn1c_to_asn1(self):
     # asn1rt
     def test_asn1rt(self):
         print('[<>] testing pycrate_asn1rt')
+        test_setobj_intersect()
         test_rt_base()
         test_rrc3g()
         test_lteran()