diff --git a/lib/galaxy/model/__init__.py b/lib/galaxy/model/__init__.py
index 2db0fce90455..7eb5fa19338e 100644
--- a/lib/galaxy/model/__init__.py
+++ b/lib/galaxy/model/__init__.py
@@ -3000,7 +3000,7 @@ class ChatExchangeMessage(Base, RepresentById):
 
     id: Mapped[int] = mapped_column(primary_key=True)
     chat_exchange_id: Mapped[int] = mapped_column(ForeignKey("chat_exchange.id"), index=True)
-    create_time: Mapped[datetime] = mapped_column(default=now, nullable=True)
+    create_time: Mapped[datetime] = mapped_column(default=now)
     message: Mapped[str] = mapped_column(Text)
     feedback: Mapped[Optional[int]] = mapped_column(Integer)
     chat_exchange: Mapped["ChatExchange"] = relationship("ChatExchange", back_populates="messages")