diff --git a/README.md b/README.md
index b4da26e9..3755e959 100644
--- a/README.md
+++ b/README.md
@@ -581,6 +581,28 @@ class CollectionSelectInput < SimpleForm::Inputs::CollectionSelectInput
 end
 ```
 
+If needed, you can namespace your custom inputs in a module and tell **SimpleForm** to look for
+their definition in this module. This can avoid conflicts with other form libraries (like Formtastic) that look up
+the global context to find inputs definition too.
+
+```ruby
+# app/inputs/custom_inputs/numeric_input
+module CustomInputs
+  class NumericInput < SimpleForm::Inputs::NumericInput
+    def input_html_classes
+      super.push('no-spinner')
+    end
+  end
+end
+```
+
+And in the **SimpleForm** initializer :
+
+```ruby
+# config/simple_form.rb
+config.custom_inputs_namespaces << "CustomInputs"
+```
+
 ## Custom form builder
 
 You can create a custom form builder that uses **Simple Form**.
diff --git a/lib/generators/simple_form/templates/config/initializers/simple_form.rb b/lib/generators/simple_form/templates/config/initializers/simple_form.rb
index bf7be1cc..2427d4a3 100644
--- a/lib/generators/simple_form/templates/config/initializers/simple_form.rb
+++ b/lib/generators/simple_form/templates/config/initializers/simple_form.rb
@@ -131,6 +131,10 @@ SimpleForm.setup do |config|
   # type as key and the wrapper that will be used for all inputs with specified type.
   # config.wrapper_mappings = { string: :prepend }
 
+  # Namespaces where SimpleForm should look for custom input classes that
+  # override default inputs.
+  # config.custom_inputs_namespaces << "CustomInputs"
+
   # Default priority for time_zone inputs.
   # config.time_zone_priority = nil
 
diff --git a/lib/simple_form.rb b/lib/simple_form.rb
index 02b01fa7..76b9b74a 100644
--- a/lib/simple_form.rb
+++ b/lib/simple_form.rb
@@ -130,6 +130,14 @@ See https://github.com/plataformatec/simple_form/pull/997 for more information.
   mattr_accessor :wrapper_mappings
   @@wrapper_mappings = nil
 
+  # Namespaces where SimpleForm should look for custom input classes that override
+  # default inputs. Namespaces are given as string to allow lazy loading inputs
+  # e.g. config.custom_inputs_namespaces << "CustomInputs"
+  #      will try to find CustomInputs::NumericInput when an :integer
+  #      field is called
+  mattr_accessor :custom_inputs_namespaces
+  @@custom_inputs_namespaces = []
+
   # Default priority for time_zone inputs.
   mattr_accessor :time_zone_priority
   @@time_zone_priority = nil
diff --git a/lib/simple_form/form_builder.rb b/lib/simple_form/form_builder.rb
index 5d06aa4d..e9df4f49 100644
--- a/lib/simple_form/form_builder.rb
+++ b/lib/simple_form/form_builder.rb
@@ -567,6 +567,7 @@ module SimpleForm
         else
           camelized = "#{input_type.to_s.camelize}Input"
           attempt_mapping(camelized, Object) || attempt_mapping(camelized, self.class) ||
+            attempt_mapping_with_custom_namespace(camelized) ||
             raise("No input found for #{input_type}")
         end
     end
@@ -604,7 +605,9 @@ module SimpleForm
     def mapping_override(klass)
       name = klass.name
       if name =~ /^SimpleForm::Inputs/
-        attempt_mapping name.split("::").last, Object
+        input_name = name.split("::").last
+        attempt_mapping(input_name, Object) ||
+          attempt_mapping_with_custom_namespace(input_name)
       end
     end
 
@@ -617,5 +620,17 @@ module SimpleForm
         raise if e.message !~ /#{mapping}$/
       end
     end
+
+    def attempt_mapping_with_custom_namespace(input_name)
+      SimpleForm.custom_inputs_namespaces.each do |namespace|
+        camelized = [namespace, input_name].join("::")
+
+        if (mapping = attempt_mapping(camelized, Object))
+          return mapping
+        end
+      end
+
+      nil
+    end
   end
 end
diff --git a/test/inputs/discovery_test.rb b/test/inputs/discovery_test.rb
index dc97d984..1fcebefb 100644
--- a/test/inputs/discovery_test.rb
+++ b/test/inputs/discovery_test.rb
@@ -14,6 +14,8 @@ class DiscoveryTest < ActionView::TestCase
         Object.send :remove_const, :CustomizedInput
         Object.send :remove_const, :DeprecatedInput
         Object.send :remove_const, :CollectionSelectInput
+        CustomInputs.send :remove_const, :PasswordInput
+        CustomInputs.send :remove_const, :NumericInput
       end
     end
   end
@@ -61,6 +63,24 @@ class DiscoveryTest < ActionView::TestCase
     end
   end
 
+  test 'builder discovers new inputs from configured namespaces if not cached' do
+    discovery do
+      swap SimpleForm, custom_inputs_namespaces: ['CustomInputs'] do
+        with_form_for @user, :password, as: :password
+        assert_select 'form input#user_password.password-custom-input'
+      end
+    end
+  end
+
+  test 'builder discovers new inputs from top level namespace before the ones from configured namespaces' do
+    discovery do
+      swap SimpleForm, custom_inputs_namespaces: ['CustomInputs'] do
+        with_form_for @user, :age
+        assert_no_select 'form input#user_age.numeric-custom-input'
+      end
+    end
+  end
+
   test 'new inputs can override the input_html_options' do
     discovery do
       with_form_for @user, :active, as: :select
diff --git a/test/support/discovery_inputs.rb b/test/support/discovery_inputs.rb
index eebf4db8..c627f6f4 100644
--- a/test/support/discovery_inputs.rb
+++ b/test/support/discovery_inputs.rb
@@ -35,3 +35,17 @@ class CollectionSelectInput < SimpleForm::Inputs::CollectionSelectInput
     super.push('chosen')
   end
 end
+
+module CustomInputs
+  class PasswordInput < SimpleForm::Inputs::PasswordInput
+    def input_html_classes
+      super.push('password-custom-input')
+    end
+  end
+
+  class NumericInput < SimpleForm::Inputs::PasswordInput
+    def input_html_classes
+      super.push('numeric-custom-input')
+    end
+  end
+end
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