diff --git a/micall/core/contig_stitcher.py b/micall/core/contig_stitcher.py
index cf4c382fa..150022506 100644
--- a/micall/core/contig_stitcher.py
+++ b/micall/core/contig_stitcher.py
@@ -287,9 +287,8 @@ def find_most_covered(contigs) -> Optional[AlignedContig]:
 def split_contigs_with_gaps(contigs: List[AlignedContig]) -> Iterable[AlignedContig]:
     def covered_by(gap, contig):
         # TODO(vitalik): implement the more precise check
-        possible_reference_coordinates = set(range(gap.r_st, gap.r_ei + 1))
-        return possible_reference_coordinates \
-                .issubset(contig.alignment.coordinate_mapping.reference_coordinates())
+        return gap.coordinate_mapping.all_reference_coordinates() \
+                .issubset(contig.alignment.coordinate_mapping.mapped_reference_coordinates())
 
     def covered(contig, gap):
         return any(covered_by(gap, other) for other in contigs
diff --git a/micall/tests/test_cigar_tools.py b/micall/tests/test_cigar_tools.py
index b61912207..65591f539 100644
--- a/micall/tests/test_cigar_tools.py
+++ b/micall/tests/test_cigar_tools.py
@@ -30,13 +30,13 @@
     ('5M3I4M', {0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 8, 6: 9, 7: 10, 8: 11},
                {0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 8, 6: 9, 7: 10, 8: 11}),
     ('1M1D',   {0: 0},
-               {0: 0}),
+               {0: 0, 1: 0}),
     ('1M1I',   {0: 0},
                {0: 0}),
     ('1I1M',   {0: 1},
                {0: 1}),
     ('1D1M',   {1: 0},
-               {1: 0}),
+               {1: 0, 0: 0}),
 
     # Multiple deletions and insertions
     ('2M2D2M2I2M', {0: 0, 1: 1, 4: 2, 5: 3, 6: 6, 7: 7},
@@ -62,7 +62,8 @@ def test_cigar_to_coordinate_mapping(cigar_str, expected_mapping):
     mapping = Cigar.coerce(cigar_str).coordinate_mapping
 
     assert expected_mapping == mapping.ref_to_query_d
-    assert expected_mapping == {i: mapping.ref_to_query(i) for i in mapping.reference_coordinates()}
+    assert expected_mapping == {i: mapping.ref_to_query(i)
+                                for i in mapping.mapped_reference_coordinates()}
 
 
 @pytest.mark.parametrize("cigar_str", [x[0] for x in cigar_mapping_cases])
@@ -86,9 +87,8 @@ def test_cigar_to_closest_coordinate_mapping(cigar_str, expected_closest_mapping
             mapping.ref_to_closest_query(0)
 
     else:
-        fullrange = {i: mapping.ref_to_closest_query(i) \
-                     for i in range(min(mapping.reference_coordinates()),
-                                    1 + max(mapping.reference_coordinates()))}
+        fullrange = {i: mapping.ref_to_closest_query(i)
+                     for i in mapping.all_reference_coordinates()}
         assert expected_closest_mapping == fullrange
 
 
@@ -103,7 +103,8 @@ def test_cigar_hit_to_coordinate_mapping(cigar_str, expected_mapping):
     assert mapping.ref_to_query(0) == None
     assert mapping.query_to_ref(0) == None
     assert expected_mapping \
-        == {i: mapping.ref_to_query(i) for i in mapping.reference_coordinates()}
+        == {i: mapping.ref_to_query(i)
+            for i in mapping.mapped_reference_coordinates()}
 
 
 @pytest.mark.parametrize("cigar_str, expected_closest_mapping", [(x[0], x[2]) for x in cigar_mapping_cases])
@@ -119,9 +120,8 @@ def test_cigar_hit_to_coordinate_closest_mapping(cigar_str, expected_closest_map
     else:
         # Coordinates are translated by q_st and r_st.
         expected_closest_mapping = {k + hit.r_st: v + hit.q_st for (k, v) in expected_closest_mapping.items()}
-        fullrange = {i: mapping.ref_to_closest_query(i) \
-                     for i in range(min(mapping.reference_coordinates()),
-                                    1 + max(mapping.reference_coordinates()))}
+        fullrange = {i: mapping.ref_to_closest_query(i)
+                     for i in mapping.all_reference_coordinates()}
         assert expected_closest_mapping == fullrange
 
 
diff --git a/micall/utils/cigar_tools.py b/micall/utils/cigar_tools.py
index 0de61b76f..48b428e03 100644
--- a/micall/utils/cigar_tools.py
+++ b/micall/utils/cigar_tools.py
@@ -60,14 +60,22 @@ def extend(self,
                 self.query_to_op_d[query_index] = op_index
 
 
-    def reference_coordinates(self) -> Set[int]:
+    def mapped_reference_coordinates(self) -> Set[int]:
         return set(self.ref_to_query_d.keys())
 
 
-    def query_coordinates(self) -> Set[int]:
+    def all_reference_coordinates(self) -> Set[int]:
+        return set(self.ref_to_op_d.keys())
+
+
+    def mapped_query_coordinates(self) -> Set[int]:
         return set(self.query_to_ref_d.keys())
 
 
+    def all_query_coordinates(self) -> Set[int]:
+        return set(self.query_to_op_d.keys())
+
+
     def ref_to_query(self, index) -> Optional[int]:
         return self.ref_to_query_d.get(index, None)
 
@@ -373,8 +381,8 @@ def intervals_overlap(x, y):
     def gaps(self) -> Iterable['CigarHit']:
         # TODO(vitalik): memoize whatever possible.
 
-        covered_coordinates = self.coordinate_mapping.reference_coordinates()
-        all_coordinates = range(self.r_st, self.r_ei + 1)
+        covered_coordinates = self.coordinate_mapping.mapped_reference_coordinates()
+        all_coordinates = self.coordinate_mapping.all_reference_coordinates()
 
         def make_gap(r_st, r_en):
             r_ei = r_en - 1