From 8c7ea033397b2999434d115c90222e829a5f5bf3 Mon Sep 17 00:00:00 2001
From: Miro <200482516+Mirochill@users.noreply.github.com>
Date: Wed, 27 May 2026 10:59:56 +0200
Subject: [PATCH] Reject negative plate sizes

---
 pyro/poutine/subsample_messenger.py | 2 ++
 tests/test_primitives.py            | 5 +++++
 2 files changed, 7 insertions(+)

diff --git a/pyro/poutine/subsample_messenger.py b/pyro/poutine/subsample_messenger.py
index 5fe9203aea..bc8a88a562 100644
--- a/pyro/poutine/subsample_messenger.py
+++ b/pyro/poutine/subsample_messenger.py
@@ -115,6 +115,8 @@ def _subsample(
             size = -1  # This is PyTorch convention for "arbitrary size"
             subsample_size = -1
         else:
+            if size < 0:
+                raise ValueError("size cannot be negative")
             msg = Message(
                 type="sample",
                 name=name,
diff --git a/tests/test_primitives.py b/tests/test_primitives.py
index c208a2cfa2..e7f4063218 100644
--- a/tests/test_primitives.py
+++ b/tests/test_primitives.py
@@ -36,6 +36,11 @@ def test_deterministic_ok():
     assert x.shape == ()
 
 
+def test_plate_negative_size_error():
+    with pytest.raises(ValueError, match="size cannot be negative"):
+        pyro.plate("data", -1)
+
+
 @pytest.mark.parametrize(
     "mask",
     [