diff --git a/lib/galaxy/tools/parameters/basic.py b/lib/galaxy/tools/parameters/basic.py
index 05cbb2c6b8d..ef01c27f7f6 100644
--- a/lib/galaxy/tools/parameters/basic.py
+++ b/lib/galaxy/tools/parameters/basic.py
@@ -1117,6 +1117,17 @@ class SelectToolParameter(ToolParameter):
                         )
             if is_runtime_value(value):
                 return None
+            if isinstance(value, dict):
+                # A dict is unhashable and can never be a legal value, but
+                # testing membership against the set of legal values would
+                # raise an opaque "unhashable type" TypeError. Treat it as an
+                # invalid option instead.
+                raise ParameterValueError(
+                    f"an invalid option ({value!r}) was selected (valid options: {','.join(iter_to_string(legal_values))})",
+                    self.name,
+                    value,
+                    is_dynamic=self.is_dynamic,
+                )
             if value in legal_values:
                 return value
             elif value in fallback_values:
diff --git a/test/unit/app/tools/test_select_parameters.py b/test/unit/app/tools/test_select_parameters.py
index 6c9fcaa38f1..b24ba677211 100644
--- a/test/unit/app/tools/test_select_parameters.py
+++ b/test/unit/app/tools/test_select_parameters.py
@@ -26,6 +26,14 @@ class TestSelectToolParameter(BaseParameterTestCase):
             self.param.from_json("42", self.trans)
         assert str(exc_info.value) == "Parameter 'my_name': requires a value, but no legal values defined"
 
+    def test_dict_value_is_invalid_option(self):
+        # A dict value is unhashable; checking it against the set of legal
+        # values used to raise an opaque "unhashable type: 'dict'" TypeError.
+        param = self._parameter_for(xml="""<param name="my_name" type="select"><option value="a">A</option></param>""")
+        with pytest.raises(ValueError) as exc_info:
+            param.from_json({"not": "valid"}, self.trans)
+        assert "an invalid option" in str(exc_info.value)
+
     def test_unvalidated_values(self):
         self.options_xml = """<options><filter type="data_meta" ref="input_bam" key="dbkey"/></options>"""
         self.trans.workflow_building_mode = True