diff --git a/aiidalab_widgets_base/structures.py b/aiidalab_widgets_base/structures.py
index c3f4ecea8..d72b3b4f6 100644
--- a/aiidalab_widgets_base/structures.py
+++ b/aiidalab_widgets_base/structures.py
@@ -312,6 +312,7 @@ def _observe_input_structure(self, change):
         # If the `input_structure` trait is set to Atoms object, then the `structure` trait should be set to it as well.
         self.history = []
 
+        self.structure = None
         if isinstance(change["new"], ase.Atoms):
             self.structure = change["new"]
 
@@ -327,9 +328,6 @@ def _observe_input_structure(self, change):
         elif isinstance(change["new"], StructureData):
             self.structure = change["new"].get_ase()
 
-        else:
-            self.structure = None
-
     @tl.observe("structure")
     def _structure_changed(self, change=None):
         """Perform some operations that depend on the value of `structure` trait.
@@ -408,6 +406,7 @@ def _validate_and_fix_ase_cell(self, ase_structure, vacuum_ang=10.0):
 
     def _on_file_upload(self, change=None):
         """When file upload button is pressed."""
+        self.structure = None
         for fname, item in change["new"].items():
             self.structure = self._read_structure(fname, item["content"])
             self.file_upload.value.clear()
@@ -782,6 +781,7 @@ def _on_button_pressed(self, change=None):
         """Convert SMILES to ASE structure when button is pressed."""
         self.output.value = ""
 
+        self.structure = None
         if not self.smiles.value:
             return
         spinner = f"Screening possible conformers {self.SPINNER}"  # font-size:20em;