diff --git a/src/openscad_parser/ast/nodes.py b/src/openscad_parser/ast/nodes.py
index 4a1649e..d5fa330 100644
--- a/src/openscad_parser/ast/nodes.py
+++ b/src/openscad_parser/ast/nodes.py
@@ -393,6 +393,11 @@ class RangeLiteral(Primary):
     step: Expression
 
     def __str__(self):
+        # A synthesised default step (2-arg source range) is tagged with the
+        # range node's own position; an explicit third argument has a distinct
+        # source position.
+        if self.step.position == self.position:
+            return f"[{self.start} : {self.end}]"
         return f"[{self.start} : {self.end} : {self.step}]"
 
     def build_scope(self, parent_scope: "Scope") -> None:
diff --git a/tests/test_nodes.py b/tests/test_nodes.py
index 7ca5797..62f7c26 100644
--- a/tests/test_nodes.py
+++ b/tests/test_nodes.py
@@ -172,8 +172,15 @@ def test_primary_and_range_str():
     member = PrimaryMember(left=_ident("obj"), member=_ident("x"), position=_pos())
     assert str(member) == "obj.x"
 
-    range_lit = RangeLiteral(start=_num(0.0), end=_num(5.0), step=_num(1.0), position=_pos())
-    assert str(range_lit) == "[0 : 5 : 1]"
+    # 2-arg: step shares range position (synthesised default) → omit step
+    range_2arg = RangeLiteral(start=_num(0.0), end=_num(5.0), step=_num(1.0), position=_pos())
+    assert str(range_2arg) == "[0:5]"
+
+    # 3-arg: step has a distinct position (explicit in source) → include step
+    step_pos = Position(origin="<test>", line=1, column=5)
+    step_explicit = NumberLiteral(val=2.0, position=step_pos)
+    range_3arg = RangeLiteral(start=_num(0.0), end=_num(5.0), step=step_explicit, position=_pos())
+    assert str(range_3arg) == "[0: 5 : 2]"
 
 
 def test_list_comprehension_str():
diff --git a/tests/test_pretty_print.py b/tests/test_pretty_print.py
index e46a926..b9b5cb3 100644
--- a/tests/test_pretty_print.py
+++ b/tests/test_pretty_print.py
@@ -398,7 +398,7 @@ def test_assert_no_child(self):
 class TestListCompForFormatting:
     def test_short_for_expands(self):
         out = _fmt("x = [for (i = [0:3]) i];")
-        assert out == "x = [\n        for (i = [0 : 3 : 1])\n            i\n    ];"
+        assert out == "x = [\n        for (i = [0 : 3])\n            i\n    ];"
 
     def test_long_for_body_on_new_line(self):
         out = _fmt("x = [for (long_variable_name = [start_value:step_value:end_value]) long_variable_name * scaling_factor_x];")
@@ -408,7 +408,7 @@ def test_long_for_body_on_new_line(self):
     def test_long_for_assignments_multiline(self):
         out = _fmt("x = [for (very_long_variable_name_alpha = [start_value:end_value], very_long_variable_name_beta = [0:10]) very_long_variable_name_alpha];")
         assert "for (\n" in out
-        assert "            very_long_variable_name_alpha = [start_value : end_value : 1]," in out
+        assert "            very_long_variable_name_alpha = [start_value : end_value]," in out
         assert ")\n" in out
 
     def test_nested_for(self):
diff --git a/tests/test_vectors.py b/tests/test_vectors.py
index 1915e2f..9d3321c 100644
--- a/tests/test_vectors.py
+++ b/tests/test_vectors.py
@@ -68,6 +68,39 @@ def test_range_expressions(self, parser):
         code = "x = [0:2*5:10];"
         parse_success(parser, code)
 
+    def test_range_two_arg_round_trip(self):
+        """Two-argument range [start:end] must not gain a spurious :1 after round-trip."""
+        import tempfile
+        import os
+        from openscad_parser.ast import getASTfromFile
+        from openscad_parser.ast.pretty_print import to_openscad
+        code = "x = [for(i = [0:5]) i];"
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.scad', delete=False) as f:
+            f.write(code)
+            fname = f.name
+        output = to_openscad(getASTfromFile(fname, process_includes=False))
+        os.unlink(fname)
+        assert ":1]" not in output, f"Spurious step in output: {output!r}"
+        assert "[0:5]" in output
+
+    def test_range_three_arg_round_trip(self):
+        """Three-argument range [start:step:end] must preserve all three arguments."""
+        import tempfile
+        import os
+        from openscad_parser.ast import getASTfromFile
+        from openscad_parser.ast.pretty_print import to_openscad
+        cases = [
+            ("x = [for(i = [10:-1:0]) i];", "[10:-1:0]"),
+            ("x = [for(i = [0:1:4]) i];",   "[0:1:4]"),
+        ]
+        for src, expected in cases:
+            with tempfile.NamedTemporaryFile(mode='w', suffix='.scad', delete=False) as f:
+                f.write(src)
+                fname = f.name
+            output = to_openscad(getASTfromFile(fname, process_includes=False))
+            os.unlink(fname)
+            assert expected in output, f"{src!r} → missing {expected!r} in {output!r}"
+
 
 class TestListComprehensionFor:
     """Test list comprehension with for."""