diff --git a/dataclasses_json/core.py b/dataclasses_json/core.py
index 7901e80d..3dafe9f9 100644
--- a/dataclasses_json/core.py
+++ b/dataclasses_json/core.py
@@ -310,8 +310,22 @@ def _decode_generic(type_, value, infer_missing):
                 res = _decode_generic(type_arg, value, infer_missing)
             else:
                 res = _support_extended_types(type_arg, value)
-        else:  # Union (already decoded or unsupported 'from_json' used)
-            res = value
+        else:  # Union (already decoded or try to decode a dataclass)
+            type_options = _get_type_args(type_)
+            res = value  # assume already decoded
+            if type(value) is dict and dict not in type_options:
+                # FIXME if all types in the union are dataclasses this
+                #  will just pick the first option -
+                #  maybe find the best fitting class in that case instead?
+                for type_option in type_options:
+                    if is_dataclass(type_option):
+                        res = _decode_dataclass(type_option, value, infer_missing)
+                        break
+                if res == value:
+                    warnings.warn(
+                        f"Failed to encode {value} Union dataclasses."
+                        f"Expected Union to include a dataclass and it didn't."
+                    )
     return res
 
 
diff --git a/tests/test_collection_of_unions.py b/tests/test_collection_of_unions.py
new file mode 100644
index 00000000..598c22d3
--- /dev/null
+++ b/tests/test_collection_of_unions.py
@@ -0,0 +1,172 @@
+from dataclasses import dataclass
+from typing import Dict, Union, List
+import json
+
+from dataclasses_json import dataclass_json
+
+
+@dataclass_json
+@dataclass(frozen=True)
+class TestChild:
+    some_field: int = None
+
+
+@dataclass_json
+@dataclass(frozen=True)
+class TestOtherChild:
+    other_field: int = None
+
+
+@dataclass_json
+@dataclass(frozen=True)
+class DictUnion:
+    d: Dict[str, Union[TestChild, TestOtherChild]]
+
+
+@dataclass_json
+@dataclass(frozen=True)
+class ListUnion:
+    l: List[Union[TestChild, TestOtherChild]]
+
+
+@dataclass_json
+@dataclass(frozen=True)
+class Player:
+    name: str
+
+
+@dataclass_json
+@dataclass(frozen=True)
+class Team:
+    roster: List[Union[int, Player]]
+    roster_backup: Dict[int, Union[int, Player]]
+
+
+class TestCollectionOfUnions:
+    def test_dict(self):
+        data = {
+            'd': {
+                'child' : {
+                    'some_field' : 1
+                },
+                'other_child' : {
+                    'other_field' : 2
+                }
+            }
+        }
+        json_str = json.dumps(data)
+        obj = DictUnion.from_json(json_str)
+
+        assert type(obj.d['child']) in (TestChild, TestOtherChild)
+
+    def test_list(self):
+        data = {
+            'l': [
+                {
+                    'some_field' : 1
+                },
+                {
+                    'other_field' : 1
+                }
+            ]
+        }
+        json_str = json.dumps(data)
+        obj = ListUnion.from_json(json_str)
+
+        assert type(obj.l[0]) in (TestChild, TestOtherChild)
+
+    def test_int(self):
+        data = {
+            'roster': [
+                1,
+                2,
+                3
+            ],
+            'roster_backup': {
+                1: 5,
+                2: 3,
+                3: 2
+            }
+        }
+        json_str = json.dumps(data)
+        obj: Team = Team.from_json(json_str)
+
+        assert type(obj.roster[0]) is int and type(obj.roster_backup[1]) is int
+
+    def test_dataclass(self):
+        data = {
+            'roster': [
+                {
+                    'name': 'player1'
+                },
+                {
+                    'name': 'player2'
+                },
+                {
+                    'name': 'player3'
+                }
+            ],
+            'roster_backup': {
+                1: {
+                    'name': 'player1'
+                },
+                2: {
+                    'name': 'player2'
+                },
+                3: {
+                    'name': 'player3'
+                }
+            }
+        }
+        json_str = json.dumps(data)
+        obj: Team = Team.from_json(json_str)
+
+        assert type(obj.roster[0]) is Player and type(obj.roster_backup[1]) is Player
+
+    def test_mixed(self):
+        data = {
+            'roster': [
+                {
+                    'name': 'player1'
+                },
+                {
+                    'name': 'player2'
+                },
+                {
+                    'name': 'player3'
+                }
+            ],
+            'roster_backup': {
+                1: 5,
+                2: 3,
+                3: 2
+            }
+        }
+        json_str = json.dumps(data)
+        obj: Team = Team.from_json(json_str)
+
+        assert type(obj.roster[0]) is Player and type(obj.roster_backup[1]) is int
+
+    def test_mixed_inverse(self):
+        data = {
+            'roster': [
+                1,
+                2,
+                3
+            ],
+            'roster_backup': {
+                1: {
+                    'name': 'player1'
+                },
+                2: {
+                    'name': 'player2'
+                },
+                3: {
+                    'name': 'player3'
+                }
+            }
+        }
+        json_str = json.dumps(data)
+        obj: Team = Team.from_json(json_str)
+
+        assert type(obj.roster[0]) is int and type(obj.roster_backup[1]) is Player