diff --git a/mypy/plugins/attrs.py b/mypy/plugins/attrs.py
index 78afc422add6..d97e92875977 100644
--- a/mypy/plugins/attrs.py
+++ b/mypy/plugins/attrs.py
@@ -13,7 +13,7 @@
     TupleExpr, ListExpr, NameExpr, CallExpr, RefExpr, FuncDef,
     is_class_var, TempNode, Decorator, MemberExpr, Expression,
     SymbolTableNode, MDEF, JsonDict, OverloadedFuncDef, ARG_NAMED_OPT, ARG_NAMED,
-    TypeVarExpr
+    TypeVarExpr, PlaceholderNode
 )
 from mypy.plugins.common import (
     _get_argument, _get_bool_argument, _get_decorator_bool_argument, add_method
@@ -270,6 +270,9 @@ def _analyze_class(ctx: 'mypy.plugin.ClassDefContext',
         # instance level assignments.
         if attribute.name in ctx.cls.info.names:
             node = ctx.cls.info.names[attribute.name].node
+            if isinstance(node, PlaceholderNode):
+                # This node is not ready yet.
+                continue
             assert isinstance(node, Var)
             node.is_initialized_in_class = False
 
diff --git a/mypy/plugins/dataclasses.py b/mypy/plugins/dataclasses.py
index dbe3695bf260..5e9a895d803a 100644
--- a/mypy/plugins/dataclasses.py
+++ b/mypy/plugins/dataclasses.py
@@ -8,7 +8,7 @@
 from mypy.nodes import (
     ARG_OPT, ARG_POS, MDEF, Argument, AssignmentStmt, CallExpr,
     Context, Expression, FuncDef, JsonDict, NameExpr, RefExpr,
-    SymbolTableNode, TempNode, TypeInfo, Var, TypeVarExpr
+    SymbolTableNode, TempNode, TypeInfo, Var, TypeVarExpr, PlaceholderNode
 )
 from mypy.plugin import ClassDefContext
 from mypy.plugins.common import add_method, _get_decorator_bool_argument
@@ -214,6 +214,9 @@ def collect_attributes(self) -> List[DataclassAttribute]:
                 continue
 
             node = cls.info.names[lhs.name].node
+            if isinstance(node, PlaceholderNode):
+                # This node is not ready yet.
+                continue
             assert isinstance(node, Var)
 
             # x: ClassVar[int] is ignored by dataclasses.
diff --git a/test-data/unit/check-attr.test b/test-data/unit/check-attr.test
index 6202b4e6aed4..070528b7495a 100644
--- a/test-data/unit/check-attr.test
+++ b/test-data/unit/check-attr.test
@@ -1107,3 +1107,47 @@ C(43)
 
 class Yes: ...
 [builtins fixtures/exception.pyi]
+
+[case testTypeInAttrUndefined]
+import attr
+
+@attr.s
+class C:
+    total = attr.ib(type=Bad)  # E: Name 'Bad' is not defined
+[builtins fixtures/bool.pyi]
+
+[case testTypeInAttrForwardInRuntime]
+import attr
+
+@attr.s
+class C:
+    total = attr.ib(type=Forward)
+
+reveal_type(C.total)  # N: Revealed type is '__main__.Forward'
+C('no')  # E: Argument 1 to "C" has incompatible type "str"; expected "Forward"
+class Forward: ...
+[builtins fixtures/bool.pyi]
+
+[case testDefaultInAttrForward]
+import attr
+
+@attr.s
+class C:
+    total = attr.ib(default=func())
+
+def func() -> int: ...
+
+C()
+C(1)
+C(1, 2)  # E: Too many arguments for "C"
+[builtins fixtures/bool.pyi]
+
+[case testTypeInAttrUndefinedFrozen]
+import attr
+
+@attr.s(frozen=True)
+class C:
+    total = attr.ib(type=Bad)  # E: Name 'Bad' is not defined
+
+C(0).total = 1  # E: Property "total" defined in "C" is read-only
+[builtins fixtures/bool.pyi]
diff --git a/test-data/unit/check-dataclasses.test b/test-data/unit/check-dataclasses.test
index cac18b239d62..5150c257b2fd 100644
--- a/test-data/unit/check-dataclasses.test
+++ b/test-data/unit/check-dataclasses.test
@@ -642,3 +642,26 @@ a < b
 
 class Yes: ...
 [builtins fixtures/list.pyi]
+
+[case testDataclassFieldDeferred]
+from dataclasses import field, dataclass
+
+@dataclass
+class C:
+    x: int = field(default=func())
+
+def func() -> int: ...
+C('no')  # E: Argument 1 to "C" has incompatible type "str"; expected "int"
+[builtins fixtures/bool.pyi]
+
+[case testDataclassFieldDeferredFrozen]
+from dataclasses import field, dataclass
+
+@dataclass(frozen=True)
+class C:
+    x: int = field(default=func())
+
+def func() -> int: ...
+c: C
+c.x = 1  # E: Property "x" defined in "C" is read-only
+[builtins fixtures/bool.pyi]