diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 5381a3b17f..fd6969cd3d 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -2,7 +2,6 @@ import collections.abc
 import copy
 import datetime
 import decimal
-import math
 import operator
 import uuid
 import warnings
@@ -1703,22 +1702,24 @@ class DecimalField(Field):
     def to_python(self, value):
         if value is None:
             return value
-        if isinstance(value, float):
-            if math.isnan(value):
-                raise exceptions.ValidationError(
-                    self.error_messages["invalid"],
-                    code="invalid",
-                    params={"value": value},
-                )
-            return self.context.create_decimal_from_float(value)
         try:
-            return decimal.Decimal(value)
+            if isinstance(value, float):
+                decimal_value = self.context.create_decimal_from_float(value)
+            else:
+                decimal_value = decimal.Decimal(value)
         except (decimal.InvalidOperation, TypeError, ValueError):
             raise exceptions.ValidationError(
                 self.error_messages["invalid"],
                 code="invalid",
                 params={"value": value},
             )
+        if not decimal_value.is_finite():
+            raise exceptions.ValidationError(
+                self.error_messages["invalid"],
+                code="invalid",
+                params={"value": value},
+            )
+        return decimal_value
 
     def get_db_prep_save(self, value, connection):
         return connection.ops.adapt_decimalfield_value(
diff --git a/tests/model_fields/test_decimalfield.py b/tests/model_fields/test_decimalfield.py
index 912d55af72..88c6878f59 100644
--- a/tests/model_fields/test_decimalfield.py
+++ b/tests/model_fields/test_decimalfield.py
@@ -67,10 +67,19 @@ class DecimalFieldTests(TestCase):
 
     def test_save_nan_invalid(self):
         msg = "“nan” value must be a decimal number."
-        with self.assertRaisesMessage(ValidationError, msg):
-            BigD.objects.create(d=float("nan"))
-        with self.assertRaisesMessage(ValidationError, msg):
-            BigD.objects.create(d=math.nan)
+        for value in [float("nan"), math.nan, "nan"]:
+            with self.subTest(value), self.assertRaisesMessage(ValidationError, msg):
+                BigD.objects.create(d=value)
+
+    def test_save_inf_invalid(self):
+        msg = "“inf” value must be a decimal number."
+        for value in [float("inf"), math.inf, "inf"]:
+            with self.subTest(value), self.assertRaisesMessage(ValidationError, msg):
+                BigD.objects.create(d=value)
+        msg = "“-inf” value must be a decimal number."
+        for value in [float("-inf"), -math.inf, "-inf"]:
+            with self.subTest(value), self.assertRaisesMessage(ValidationError, msg):
+                BigD.objects.create(d=value)
 
     def test_fetch_from_db_without_float_rounding(self):
         big_decimal = BigD.objects.create(d=Decimal(".100000000000000000000000000005"))