diff --git a/changes/356.bugfix.rst b/changes/356.bugfix.rst
new file mode 100644
index 00000000..faf9cfc0
--- /dev/null
+++ b/changes/356.bugfix.rst
@@ -0,0 +1 @@
+Avoid unnecessary validation on Model.__init__.
diff --git a/src/stdatamodels/jwst/datamodels/tests/test_multislit.py b/src/stdatamodels/jwst/datamodels/tests/test_multislit.py
index 27b2c65d..8fce6821 100644
--- a/src/stdatamodels/jwst/datamodels/tests/test_multislit.py
+++ b/src/stdatamodels/jwst/datamodels/tests/test_multislit.py
@@ -5,7 +5,7 @@
 from numpy.testing import assert_array_equal
 import pytest
 
-from stdatamodels.jwst.datamodels import MultiSlitModel, ImageModel
+from stdatamodels.jwst.datamodels import MultiSlitModel, ImageModel, SlitModel
 
 
 def test_multislit_model():
@@ -155,3 +155,12 @@ def test_copy_multislit():
 
     assert model1.slits[0].data[330, 330] == 1
     assert output.slits[0].data[330, 330] == -1
+
+
+def test_slit_from_multislit():
+    model = MultiSlitModel()
+    slit = SlitModel()
+    # access int_times so it's created
+    slit.int_times = slit.int_times
+    model.slits.append(slit)
+    slit = SlitModel(model.slits[0].instance)
diff --git a/src/stdatamodels/model_base.py b/src/stdatamodels/model_base.py
index a231a7d9..9042607d 100644
--- a/src/stdatamodels/model_base.py
+++ b/src/stdatamodels/model_base.py
@@ -566,6 +566,11 @@ def open_asdf(init=None,
                                  ignore_unrecognized_tag=ignore_unrecognized_tag,
                                  **kwargs)
 
+        elif isinstance(init, dict):
+            asdffile = AsdfFile(None,
+                            ignore_unrecognized_tag=ignore_unrecognized_tag
+                            )
+            asdffile._tree = init
         else:
             asdffile = AsdfFile(init,
                             ignore_unrecognized_tag=ignore_unrecognized_tag