diff --git a/nmigen/hdl/ast.py b/nmigen/hdl/ast.py
index d26c3c3..efaeb0f 100644
--- a/nmigen/hdl/ast.py
+++ b/nmigen/hdl/ast.py
@@ -8,6 +8,7 @@ from enum import Enum
 
 from .. import tracer
 from .._utils import *
+from .._unused import *
 
 
 __all__ = [
@@ -17,9 +18,9 @@ __all__ = [
     "Signal", "ClockSignal", "ResetSignal",
     "UserValue",
     "Sample", "Past", "Stable", "Rose", "Fell", "Initial",
-    "Statement", "Assign", "Assert", "Assume", "Cover", "Switch",
-    "ValueKey", "ValueDict", "ValueSet", "SignalKey", "SignalDict",
-    "SignalSet",
+    "Statement", "Switch",
+    "Property", "Assign", "Assert", "Assume", "Cover",
+    "ValueKey", "ValueDict", "ValueSet", "SignalKey", "SignalDict", "SignalSet",
 ]
 
 
@@ -493,13 +494,13 @@ class AnyValue(Value, DUID):
 @final
 class AnyConst(AnyValue):
     def __repr__(self):
-        return "(anyconst {}'{})".format(self.nbits, "s" if self.signed else "")
+        return "(anyconst {}'{})".format(self.width, "s" if self.signed else "")
 
 
 @final
 class AnySeq(AnyValue):
     def __repr__(self):
-        return "(anyseq {}'{})".format(self.nbits, "s" if self.signed else "")
+        return "(anyseq {}'{})".format(self.width, "s" if self.signed else "")
 
 
 @final
@@ -1221,7 +1222,13 @@ class Assign(Statement):
         return "(eq {!r} {!r})".format(self.lhs, self.rhs)
 
 
-class Property(Statement):
+class UnusedProperty(UnusedMustUse):
+    pass
+
+
+class Property(Statement, MustUse):
+    _MustUse__warning = UnusedProperty
+
     def __init__(self, test, *, _check=None, _en=None, src_loc_at=0):
         super().__init__(src_loc_at=src_loc_at)
         self.test   = Value.cast(test)
diff --git a/nmigen/hdl/dsl.py b/nmigen/hdl/dsl.py
index b8f7692..986ecc0 100644
--- a/nmigen/hdl/dsl.py
+++ b/nmigen/hdl/dsl.py
@@ -462,14 +462,16 @@ class Module(_ModuleBuilderRoot, Elaboratable):
         while len(self._ctrl_stack) > self.domain._depth:
             self._pop_ctrl()
 
-        for assign in Statement.cast(assigns):
-            if not compat_mode and not isinstance(assign, (Assign, Assert, Assume, Cover)):
+        for stmt in Statement.cast(assigns):
+            if not compat_mode and not isinstance(stmt, (Assign, Assert, Assume, Cover)):
                 raise SyntaxError(
                     "Only assignments and property checks may be appended to d.{}"
                     .format(domain_name(domain)))
 
-            assign = SampleDomainInjector(domain)(assign)
-            for signal in assign._lhs_signals():
+            stmt._MustUse__used = True
+            stmt = SampleDomainInjector(domain)(stmt)
+
+            for signal in stmt._lhs_signals():
                 if signal not in self._driving:
                     self._driving[signal] = domain
                 elif self._driving[signal] != domain:
@@ -479,7 +481,7 @@ class Module(_ModuleBuilderRoot, Elaboratable):
                         "already driven from d.{}"
                         .format(signal, domain_name(domain), domain_name(cd_curr)))
 
-            self._statements.append(assign)
+            self._statements.append(stmt)
 
     def _add_submodule(self, submodule, name=None):
         if not hasattr(submodule, "elaborate"):
diff --git a/nmigen/hdl/ir.py b/nmigen/hdl/ir.py
index 5d4a1c5..cea9b40 100644
--- a/nmigen/hdl/ir.py
+++ b/nmigen/hdl/ir.py
@@ -121,7 +121,9 @@ class Fragment:
         yield from self.domains
 
     def add_statements(self, *stmts):
-        self.statements += Statement.cast(stmts)
+        for stmt in Statement.cast(stmts):
+            stmt._MustUse__used = True
+            self.statements.append(stmt)
 
     def add_subfragment(self, subfragment, name=None):
         assert isinstance(subfragment, Fragment)
diff --git a/nmigen/hdl/xfrm.py b/nmigen/hdl/xfrm.py
index 75f85ba..fb4dad9 100644
--- a/nmigen/hdl/xfrm.py
+++ b/nmigen/hdl/xfrm.py
@@ -234,6 +234,8 @@ class StatementVisitor(metaclass=ABCMeta):
             new_stmt.src_loc = stmt.src_loc
             if isinstance(new_stmt, Switch) and isinstance(stmt, Switch):
                 new_stmt.case_src_locs = stmt.case_src_locs
+        if isinstance(new_stmt, Property):
+            new_stmt._MustUse__used = True
         return new_stmt
 
     def __call__(self, stmt):