diff --git a/libs/core/langchain_core/_api/deprecation.py b/libs/core/langchain_core/_api/deprecation.py
index 1c253d99215..6c0af2b8589 100644
--- a/libs/core/langchain_core/_api/deprecation.py
+++ b/libs/core/langchain_core/_api/deprecation.py
@@ -100,6 +100,16 @@ def deprecated(
                 pass
     """
 
+    if (
+        alternative_import
+        and "." not in alternative_import
+        or " " in alternative_import
+    ):
+        raise ValueError(
+            "alternative_import must be a fully qualified module path, e.g. "
+            "`package.module.Class`"
+        )
+
     def deprecate(
         obj: T,
         *,