diff --git a/src/attr/validators.py b/src/attr/validators.py
index 0b1a29443..459971422 100644
--- a/src/attr/validators.py
+++ b/src/attr/validators.py
@@ -10,6 +10,7 @@
 from contextlib import contextmanager
 from re import Pattern
 
+from ._compat import Mapping
 from ._config import get_run_validators, set_run_validators
 from ._make import _AndValidator, and_, attrib, attrs
 from .converters import default_if_none
@@ -397,6 +398,15 @@ def __call__(self, inst, attr, value):
         if self.mapping_validator is not None:
             self.mapping_validator(inst, attr, value)
 
+        if not isinstance(value, Mapping):
+            msg = f"'{attr.name}' must be a mapping (got {value!r} that is a {value.__class__!r})."
+            raise TypeError(
+                msg,
+                attr,
+                Mapping,
+                value,
+            )
+
         for key in value:
             if self.key_validator is not None:
                 self.key_validator(inst, attr, key)
diff --git a/tests/test_validators.py b/tests/test_validators.py
index 8caa64272..e4b4b9eff 100644
--- a/tests/test_validators.py
+++ b/tests/test_validators.py
@@ -807,6 +807,22 @@ def test_validators_iterables(self, conv):
         assert and_(*value_validator) == v.value_validator
         assert and_(*mapping_validator) == v.mapping_validator
 
+    def test_fail_non_mapping(self):
+        """
+        Raise TypeError if value is not a mapping.
+        """
+        key_validator = instance_of(str)
+        value_validator = instance_of(int)
+        v = deep_mapping(key_validator, value_validator)
+        a = simple_attr("test")
+        with pytest.raises(TypeError) as e:
+            v(None, a, [1, 2, 3])
+
+        msg = (
+            f"'{a.name}' must be a mapping (got [1, 2, 3] that is a {list!r})."
+        )
+        assert msg in str(e.value)
+
 
 class TestIsCallable:
     """