diff --git a/amaranth/vendor/lattice_ecp5.py b/amaranth/vendor/lattice_ecp5.py
index 288296e..4d5cb7c 100644
--- a/amaranth/vendor/lattice_ecp5.py
+++ b/amaranth/vendor/lattice_ecp5.py
@@ -231,10 +231,12 @@ class LatticeECP5Platform(TemplatedPlatform):
             # {{autogenerated}}
             BLOCK ASYNCPATHS;
             BLOCK RESETPATHS;
-            {% for port_name, pin_name, extras in platform.iter_port_constraints_bits() -%}
+            {% for port_name, pin_name, attrs in platform.iter_port_constraints_bits() -%}
                 LOCATE COMP "{{port_name}}" SITE "{{pin_name}}";
+                {% if attrs -%}
                 IOBUF PORT "{{port_name}}"
-                    {%- for key, value in extras.items() %} {{key}}={{value}}{% endfor %};
+                    {%- for key, value in attrs.items() %} {{key}}={{value}}{% endfor %};
+                {% endif %}
             {% endfor %}
             {{get_override("add_preferences")|default("# (add_preferences placeholder)")}}
         """,