diff --git a/amaranth/lib/enum.py b/amaranth/lib/enum.py
index 865e6a1..8e1d91e 100644
--- a/amaranth/lib/enum.py
+++ b/amaranth/lib/enum.py
@@ -47,7 +47,7 @@ class EnumMeta(ShapeCastable, py_enum.EnumMeta):
                         message="Value of enumeration member {!r} is signed, but enumeration "
                                 "shape is {!r}" # the repr will be `unsigned(X)`
                                 .format(member, shape),
-                        category=RuntimeWarning,
+                        category=SyntaxWarning,
                         stacklevel=2)
                 elif (member_shape.width > shape.width or
                       member_shape.width == shape.width and
@@ -56,7 +56,7 @@ class EnumMeta(ShapeCastable, py_enum.EnumMeta):
                         message="Value of enumeration member {!r} will be truncated to "
                                 "enumeration shape {!r}"
                                 .format(member, shape),
-                        category=RuntimeWarning,
+                        category=SyntaxWarning,
                         stacklevel=2)
         else:
             # Shape is not provided explicitly. Behave the same as a standard enumeration;
diff --git a/tests/test_lib_enum.py b/tests/test_lib_enum.py
index 0040fee..f7f668c 100644
--- a/tests/test_lib_enum.py
+++ b/tests/test_lib_enum.py
@@ -53,24 +53,24 @@ class EnumTestCase(FHDLTestCase):
         self.assertEqual(Shape.cast(EnumD), signed(4))
 
     def test_shape_explicit_wrong_signed_mismatch(self):
-        with self.assertWarnsRegex(RuntimeWarning,
+        with self.assertWarnsRegex(SyntaxWarning,
                 r"^Value of enumeration member <EnumA\.A: -1> is signed, but enumeration "
                 r"shape is unsigned\(1\)$"):
             class EnumA(Enum, shape=unsigned(1)):
                 A = -1
 
     def test_shape_explicit_wrong_too_wide(self):
-        with self.assertWarnsRegex(RuntimeWarning,
+        with self.assertWarnsRegex(SyntaxWarning,
                 r"^Value of enumeration member <EnumA\.A: 2> will be truncated to enumeration "
                 r"shape unsigned\(1\)$"):
             class EnumA(Enum, shape=unsigned(1)):
                 A = 2
-        with self.assertWarnsRegex(RuntimeWarning,
+        with self.assertWarnsRegex(SyntaxWarning,
                 r"^Value of enumeration member <EnumB\.A: 1> will be truncated to enumeration "
                 r"shape signed\(1\)$"):
             class EnumB(Enum, shape=signed(1)):
                 A = 1
-        with self.assertWarnsRegex(RuntimeWarning,
+        with self.assertWarnsRegex(SyntaxWarning,
                 r"^Value of enumeration member <EnumC\.A: -2> will be truncated to enumeration "
                 r"shape signed\(1\)$"):
             class EnumC(Enum, shape=signed(1)):