diff --git a/tract_querier/query_processor.py b/tract_querier/query_processor.py
index 026dbb2..84010a1 100644
--- a/tract_querier/query_processor.py
+++ b/tract_querier/query_processor.py
@@ -1,4 +1,5 @@
 import ast
+import numbers
 from os import path
 from copy import deepcopy
 from operator import lt, gt
@@ -240,12 +241,6 @@ def visit_UnaryOp(self, node):
             raise TractQuerierSyntaxError(
                 "Syntax error in query line %d" % node.lineno)
 
-    def visit_Str(self, node):
-        query_info = FiberQueryInfo()
-        for name in fnmatch.filter(self.evaluated_queries_info.keys(), node.s):
-            query_info.update(self.evaluated_queries_info[name])
-        return query_info
-
     def visit_Call(self, node):
         # Single string argument function
         if (
@@ -558,31 +553,40 @@ def visit_Attribute(self, node):
                 (node.lineno, query_name)
             )
 
-    def visit_Num(self, node):
-        if (
-            node.n in
-            self.tractography_spatial_indexing.crossing_labels_tracts
-        ):
-            tracts = (
-                self.tractography_spatial_indexing.
-                crossing_labels_tracts[node.n]
+    def visit_Constant(self, node):
+        if isinstance(node.value, numbers.Number):
+            if (
+                node.n in
+                self.tractography_spatial_indexing.crossing_labels_tracts
+            ):
+                tracts = (
+                    self.tractography_spatial_indexing.
+                    crossing_labels_tracts[node.n]
+                )
+            else:
+                tracts = set()
+
+            endpoints = (set(), set())
+            for i in (0, 1):
+                elt = self.tractography_spatial_indexing.ending_labels_tracts[i]
+                if node.n in elt:
+                    endpoints[i].update(elt[node.n])
+
+            labelset = set((node.n,))
+            query_info = FiberQueryInfo(
+                tracts, labelset,
+                endpoints
             )
-        else:
-            tracts = set()
 
-        endpoints = (set(), set())
-        for i in (0, 1):
-            elt = self.tractography_spatial_indexing.ending_labels_tracts[i]
-            if node.n in elt:
-                endpoints[i].update(elt[node.n])
-
-        labelset = set((node.n,))
-        tract_info = FiberQueryInfo(
-            tracts, labelset,
-            endpoints
-        )
+        elif isinstance(node.value, str):
+            query_info = FiberQueryInfo()
+            for name in fnmatch.filter(self.evaluated_queries_info.keys(),
+                                       node.s):
+                query_info.update(self.evaluated_queries_info[name])
+        else:
+            raise NotImplementedError(f"{node.value} not supported.")
 
-        return tract_info
+        return query_info
 
     def visit_Expr(self, node):
         if isinstance(node.value, ast.Name):
@@ -735,11 +739,14 @@ def visit_Name(self, node):
             node
         )
 
-    def visit_Str(self, node):
-        return ast.copy_location(
-            ast.Str(s=node.s.lower()),
-            node
-        )
+    def visit_Constant(self, node):
+        if isinstance(node.s, str):
+            return ast.copy_location(
+                ast.Constant(node.s.lower()),
+                node
+            )
+        else:
+            return self.generic_visit(node)
 
     def visit_Import(self, node):
         try:
diff --git a/tract_querier/tests/test_query_files.py b/tract_querier/tests/test_query_files.py
index abaa3d4..6cd669c 100644
--- a/tract_querier/tests/test_query_files.py
+++ b/tract_querier/tests/test_query_files.py
@@ -9,9 +9,12 @@
 def data_folder():
     return os.path.join(os.path.dirname(__file__), '..', 'data')
 
+#@pytest.mark.parametrize("filename", [
+#    pytest.param(os.path.join(os.path.join(os.path.dirname(__file__), '..', 'data'), f), id=f)
+#    for f in fnmatch.filter(os.listdir(os.path.join(os.path.dirname(__file__), '..', 'data')), '*qry')
+#])
 @pytest.mark.parametrize("filename", [
-    pytest.param(os.path.join(os.path.join(os.path.dirname(__file__), '..', 'data'), f), id=f)
-    for f in fnmatch.filter(os.listdir(os.path.join(os.path.dirname(__file__), '..', 'data')), '*qry')
+    "/home/jhlegarreta/src/tract_querier/tract_querier/data/debug_mori_queries_short.qry"
 ])
 def test_query_files(data_folder, filename):
     query_file_test(filename, [data_folder])