diff --git a/stl/parser.py b/stl/parser.py
index 20e8d66..4c1d2fa 100644
--- a/stl/parser.py
+++ b/stl/parser.py
@@ -67,10 +67,12 @@ _ = ~r"\s"+
 __ = ~r"\s"*
 EOL = "\\n"
 ''')
-
-default_interval = ast.Interval(0, float('inf'))
     
 class STLVisitor(NodeVisitor):
+    def __init__(self, H=float('inf')):
+        super().__init__()
+        self.default_interval = ast.Interval(0, H)
+
     def generic_visit(self, _, children):
         return children
 
@@ -94,7 +96,7 @@ class STLVisitor(NodeVisitor):
 
     def unary_temp_op_visitor(self, _, children, op):
         _, i, phi = children
-        i = default_interval if not i else i[0]
+        i = self.default_interval if not i else i[0]
         return op(i, phi)
 
     def binop_visitor(self, _, children, op):
@@ -117,7 +119,7 @@ class STLVisitor(NodeVisitor):
 
     def visit_until(self, _, children):
         _, _, phi1, _, _, i, _, phi2, *_ = children
-        i = default_interval if not i else i[0]
+        i = self.default_interval if not i else i[0]
         return ast.Until(i, phi1, phi2)
 
     def visit_id(self, name, _):
@@ -178,5 +180,5 @@ class STLVisitor(NodeVisitor):
         return ast.Neg(children[1])
 
 
-def parse(stl_str:str, rule:str="phi") -> "STL":
-    return STLVisitor().visit(STL_GRAMMAR[rule].parse(stl_str))
+def parse(stl_str:str, rule:str="phi", H=float('inf')) -> "STL":
+    return STLVisitor(H).visit(STL_GRAMMAR[rule].parse(stl_str))