diff --git a/django/forms/fields.py b/django/forms/fields.py
index 12316a1ab1..581d32d923 100644
--- a/django/forms/fields.py
+++ b/django/forms/fields.py
@@ -240,6 +240,12 @@ class DecimalField(Field):
         except DecimalException:
             raise ValidationError(self.error_messages['invalid'])
 
+        # Check for NaN, Inf and -Inf values. We can't compare directly for NaN,
+        # since it is never equal to itself. However, NaN is the only value that
+        # isn't equal to itself, so we can use this to identify NaN
+        if value != value or value == Decimal("Inf") or value == Decimal("-Inf"):
+            raise ValidationError(self.error_messages['invalid'])
+
         sign, digittuple, exponent = value.as_tuple()
         decimals = abs(exponent)
         # digittuple doesn't include any leading zeros.
diff --git a/tests/regressiontests/forms/fields.py b/tests/regressiontests/forms/fields.py
index 9d407d9ea7..48da0f9e1d 100644
--- a/tests/regressiontests/forms/fields.py
+++ b/tests/regressiontests/forms/fields.py
@@ -320,6 +320,18 @@ True
 True
 >>> f.clean(Decimal('3.14')) == Decimal("3.14")
 True
+>>> f.clean('NaN')
+Traceback (most recent call last):
+...
+ValidationError: [u'Enter a number.']
+>>> f.clean('Inf')
+Traceback (most recent call last):
+...
+ValidationError: [u'Enter a number.']
+>>> f.clean('-Inf')
+Traceback (most recent call last):
+...
+ValidationError: [u'Enter a number.']
 >>> f.clean('a')
 Traceback (most recent call last):
 ...