diff --git a/Gemfile_rails4.lock b/Gemfile_rails4.lock
index 62abe0984..15c1374f4 100644
--- a/Gemfile_rails4.lock
+++ b/Gemfile_rails4.lock
@@ -23,7 +23,7 @@ GIT
 
 GIT
   remote: git://github.com/rails/rails.git
-  revision: 0785008a64f4af8d09379683303d49d160cd444d
+  revision: 81432139a9ca5bf90f08273d88e6e4f583c4189b
   branch: 4-0-stable
   specs:
     actionmailer (4.0.0)
@@ -434,7 +434,7 @@ GEM
       multi_json (~> 1.0)
       rack (~> 1.0)
       tilt (~> 1.1, != 1.3.0)
-    sprockets-rails (2.0.0)
+    sprockets-rails (2.0.1)
       actionpack (>= 3.0)
       activesupport (>= 3.0)
       sprockets (~> 2.8)
diff --git a/app/models/screened_ip_address.rb b/app/models/screened_ip_address.rb
index 009e0efae..6822e45c3 100644
--- a/app/models/screened_ip_address.rb
+++ b/app/models/screened_ip_address.rb
@@ -21,7 +21,7 @@ class ScreenedIpAddress < ActiveRecord::Base
     #
     #   http://www.postgresql.org/docs/9.1/static/datatype-net-types.html
     #   http://www.postgresql.org/docs/9.1/static/functions-net.html
-    where('? <<= ip_address', ip_address).first
+    where("'#{ip_address.to_s}' <<= ip_address").first
   end
 
   def self.should_block?(ip_address)
diff --git a/app/services/staff_action_logger.rb b/app/services/staff_action_logger.rb
index f291ae20e..51a11d417 100644
--- a/app/services/staff_action_logger.rb
+++ b/app/services/staff_action_logger.rb
@@ -11,7 +11,7 @@ class StaffActionLogger
       action: UserHistory.actions[:delete_user],
       target_user_id: deleted_user.id,
       email: deleted_user.email,
-      ip_address: deleted_user.ip_address,
+      ip_address: deleted_user.ip_address.to_s,
       details: [:id, :username, :name, :created_at, :trust_level, :last_seen_at, :last_emailed_at].map { |x| "#{x}: #{deleted_user.send(x)}" }.join(', ')
     }))
   end
diff --git a/lib/validators/ip_address_format_validator.rb b/lib/validators/ip_address_format_validator.rb
index a08e29014..460eda40f 100644
--- a/lib/validators/ip_address_format_validator.rb
+++ b/lib/validators/ip_address_format_validator.rb
@@ -3,8 +3,16 @@
 class IpAddressFormatValidator < ActiveModel::EachValidator
 
   def validate_each(record, attribute, value)
-    unless record.ip_address.nil? or record.ip_address.split('/').first =~ Resolv::AddressRegex
-      record.errors.add(attribute, :invalid)
+    if rails4?
+      # In Rails 4, ip_address will be nil if an invalid IP address was assigned.
+      # https://github.com/jetthoughts/rails/commit/0aa95a71b04f2893921c58a7c1d9fca60dbdcbc2
+      if record.ip_address.nil?
+        record.errors.add(attribute, :invalid)
+      end
+    else
+      unless !record.ip_address.nil? and record.ip_address.to_s.split('/').first =~ Resolv::AddressRegex
+        record.errors.add(attribute, :invalid)
+      end
     end
   end
 
diff --git a/spec/components/validators/ip_address_format_validator_spec.rb b/spec/components/validators/ip_address_format_validator_spec.rb
index fa34e16e5..5f06345b5 100644
--- a/spec/components/validators/ip_address_format_validator_spec.rb
+++ b/spec/components/validators/ip_address_format_validator_spec.rb
@@ -6,7 +6,7 @@ describe IpAddressFormatValidator do
   let(:validator) { described_class.new({attributes: :ip_address}) }
   subject(:validate) { validator.validate_each(record, :ip_address, record.ip_address) }
 
-  [nil, '99.232.23.123', '99.232.0.0/16', 'fd12:db8::ff00:42:8329', 'fc00::/7'].each do |arg|
+  ['99.232.23.123', '99.232.0.0/16', 'fd12:db8::ff00:42:8329', 'fc00::/7'].each do |arg|
     it "should not add an error for #{arg}" do
       record.ip_address = arg
       validate
@@ -14,6 +14,12 @@ describe IpAddressFormatValidator do
     end
   end
 
+  it 'should add an error for nil IP address' do
+    record.ip_address = nil
+    validate
+    record.errors[:ip_address].should be_present
+  end
+
   it 'should add an error for invalid IP address' do
     record.ip_address = '99.99.99'
     validate