diff --git a/django/core/validators.py b/django/core/validators.py
index 6a8418848b5..03590a456b6 100644
--- a/django/core/validators.py
+++ b/django/core/validators.py
@@ -351,10 +351,12 @@ class IsValidFloat(object):
             float(data)
         except ValueError:
             raise ValidationError, gettext("Please enter a valid decimal number.")
-        if len(data) > (self.max_digits + 1):
+        # Negative floats require more space to input.
+        max_allowed_length = data.startswith('-') and (self.max_digits + 2) or (self.max_digits + 1)
+        if len(data) > max_allowed_length:
             raise ValidationError, ngettext("Please enter a valid decimal number with at most %s total digit.",
                 "Please enter a valid decimal number with at most %s total digits.", self.max_digits) % self.max_digits
-        if (not '.' in data and len(data) > (self.max_digits - self.decimal_places)) or ('.' in data and len(data) > (self.max_digits - (self.decimal_places - len(data.split('.')[1])) + 1)):
+        if (not '.' in data and len(data) > (self.max_allowed_length - self.decimal_places)) or ('.' in data and len(data) > (self.max_digits - (self.decimal_places - len(data.split('.')[1])) + 1)):
             raise ValidationError, ngettext( "Please enter a valid decimal number with a whole part of at most %s digit.",
                 "Please enter a valid decimal number with a whole part of at most %s digits.", str(self.max_digits-self.decimal_places)) % str(self.max_digits-self.decimal_places)
         if '.' in data and len(data.split('.')[1]) > self.decimal_places:
diff --git a/django/forms/__init__.py b/django/forms/__init__.py
index 160efe652c2..195c3576709 100644
--- a/django/forms/__init__.py
+++ b/django/forms/__init__.py
@@ -743,7 +743,7 @@ class FloatField(TextField):
         if validator_list is None: validator_list = []
         self.max_digits, self.decimal_places = max_digits, decimal_places
         validator_list = [self.isValidFloat] + validator_list
-        TextField.__init__(self, field_name, max_digits+1, max_digits+1, is_required, validator_list)
+        TextField.__init__(self, field_name, max_digits+2, max_digits+2, is_required, validator_list)
 
     def isValidFloat(self, field_data, all_data):
         v = validators.IsValidFloat(self.max_digits, self.decimal_places)