diff --git a/src/betterproto/__init__.py b/src/betterproto/__init__.py
index da6893d..c16e2cd 100644
--- a/src/betterproto/__init__.py
+++ b/src/betterproto/__init__.py
@@ -749,7 +749,7 @@ class Message(ABC):
                 group_current.setdefault(meta.group)
 
             value = self.__raw_get(field_name)
-            if value != PLACEHOLDER and not (meta.optional and value is None):
+            if value is not PLACEHOLDER and not (meta.optional and value is None):
                 # Found a non-sentinel value
                 all_sentinel = False