diff --git a/nmigen/build/plat.py b/nmigen/build/plat.py
index 291d90c..d9f2ab2 100644
--- a/nmigen/build/plat.py
+++ b/nmigen/build/plat.py
@@ -383,7 +383,8 @@ class TemplatedPlatform(Platform):
         def render(source, origin, syntax=None):
             try:
                 source   = textwrap.dedent(source).strip()
-                compiled = jinja2.Template(source, trim_blocks=True, lstrip_blocks=True)
+                compiled = jinja2.Template(source,
+                    trim_blocks=True, lstrip_blocks=True, undefined=jinja2.StrictUndefined)
                 compiled.environment.filters["options"] = options
                 compiled.environment.filters["hierarchy"] = hierarchy
             except jinja2.TemplateSyntaxError as e:
diff --git a/nmigen/vendor/lattice_ice40.py b/nmigen/vendor/lattice_ice40.py
index 56da2e8..94dd02a 100644
--- a/nmigen/vendor/lattice_ice40.py
+++ b/nmigen/vendor/lattice_ice40.py
@@ -155,7 +155,8 @@ class LatticeICE40Platform(TemplatedPlatform):
             --log {{name}}.tim
             {{platform._nextpnr_device_options[platform.device]}}
             --package
-                {{platform.package|lower}}{{platform._nextpnr_package_options[platform.device]}}
+                {{platform.package|lower}}{{platform._nextpnr_package_options[platform.device]|
+                                            default("")}}
             --json {{name}}.json
             --pcf {{name}}.pcf
             --asc {{name}}.asc