diff --git a/amaranth/hdl/_ast.py b/amaranth/hdl/_ast.py
index b3b160c..5eaf56f 100644
--- a/amaranth/hdl/_ast.py
+++ b/amaranth/hdl/_ast.py
@@ -2294,8 +2294,14 @@ class Switch(Statement):
                     key = "".join(key.split()) # remove whitespace
                 elif isinstance(key, int):
                     key = format(key & key_mask, "b").rjust(len(self.test), "0")
+                    # fixup for 0-width test
+                    if key_mask == 0:
+                        key = ""
                 elif isinstance(key, Enum):
                     key = format(key.value & key_mask, "b").rjust(len(self.test), "0")
+                    # fixup for 0-width test
+                    if key_mask == 0:
+                        key = ""
                 else:
                     raise TypeError("Object {!r} cannot be used as a switch key"
                                     .format(key))
diff --git a/tests/test_hdl_ast.py b/tests/test_hdl_ast.py
index 4b14f6b..9880ba5 100644
--- a/tests/test_hdl_ast.py
+++ b/tests/test_hdl_ast.py
@@ -1473,6 +1473,16 @@ class SwitchTestCase(FHDLTestCase):
         s = Switch(Const(0, 8), {-10: []})
         self.assertEqual(s.cases, {("11110110",): []})
 
+    def test_int_zero_width(self):
+        s = Switch(Const(0, 0), {0: []})
+        self.assertEqual(s.cases, {("",): []})
+
+    def test_int_zero_width_enum(self):
+        class ZeroEnum(Enum):
+            A = 0
+        s = Switch(Const(0, 0), {ZeroEnum.A: []})
+        self.assertEqual(s.cases, {("",): []})
+
     def test_enum_case(self):
         s = Switch(Const(0, UnsignedEnum), {UnsignedEnum.FOO: []})
         self.assertEqual(s.cases, {("01",): []})