diff --git a/src/SConscript b/src/SConscript
index 7eb810a9c2..e40262a75d 100644
--- a/src/SConscript
+++ b/src/SConscript
@@ -149,13 +149,21 @@ class SimObject(PySource):
     enums = dict()
     tags = dict()
 
-    def __init__(self, source, *, sim_objects=[], enums=[],
+    def __init__(self, source, *, sim_objects=None, enums=None,
             tags=None, add_tags=None):
         '''Specify the source file and any tags (automatically in
         the m5.objects package)'''
+        if sim_objects is None:
+            if enums is None:
+                error(f"SimObject({source}...) must list c++ sim_objects or "
+                      "enums (set either to [] if there are none).")
+            sim_objects = []
+        if enums is None:
+            enums = []
+
         super().__init__('m5.objects', source, tags, add_tags)
         if self.fixed:
-            raise AttributeError("Too late to call SimObject now.")
+            error("Too late to call SimObject now.")
 
         SimObject.sim_objects[self.modpath] = sim_objects
         SimObject.enums[self.modpath] = enums
diff --git a/src/cpu/o3/SConscript b/src/cpu/o3/SConscript
index a20e30d42d..ba021a892a 100755
--- a/src/cpu/o3/SConscript
+++ b/src/cpu/o3/SConscript
@@ -32,7 +32,7 @@ Import('*')
 
 if 'O3CPU' in env['CPU_MODELS']:
     SimObject('FUPool.py', sim_objects=['FUPool'])
-    SimObject('FuncUnitConfig.py')
+    SimObject('FuncUnitConfig.py', sim_objects=[])
     SimObject('O3CPU.py', sim_objects=['O3CPU'], enums=[
         'SMTFetchPolicy', 'SMTQueuePolicy', 'CommitPolicy'])
 
diff --git a/src/dev/SConscript b/src/dev/SConscript
index db3163e76f..755ddb541a 100644
--- a/src/dev/SConscript
+++ b/src/dev/SConscript
@@ -35,7 +35,7 @@ Source('isa_fake.cc')
 Source('dma_device.cc')
 Source('dma_virt_device.cc')
 
-SimObject('IntPin.py')
+SimObject('IntPin.py', sim_objects=[])
 Source('intpin.cc')
 
 DebugFlag('IsaFake')
diff --git a/src/systemc/SConscript b/src/systemc/SConscript
index ef7e79b69d..57cb1d947d 100644
--- a/src/systemc/SConscript
+++ b/src/systemc/SConscript
@@ -32,4 +32,4 @@ env.UseSystemcCheck(warn=True)
 
 env.Append(CPPPATH=Dir('ext'))
 
-SimObject('Tlm.py')
+SimObject('Tlm.py', sim_objects=[])