diff --git a/sygnal/gcmpushkin.py b/sygnal/gcmpushkin.py
index 1177c0aa..621c2fd7 100644
--- a/sygnal/gcmpushkin.py
+++ b/sygnal/gcmpushkin.py
@@ -669,7 +669,7 @@ def _build_data(
                     data[attr] = data[attr][0:MAX_BYTES_PER_FIELD]
 
         if api_version is APIVersion.V1:
-            if "content" in data:
+            if isinstance(data.get("content"), dict):
                 for attr, value in data["content"].items():
                     if not isinstance(value, str):
                         continue