diff --git a/modules/field/field.api.php b/modules/field/field.api.php
index 9c52d24..0790f0b 100644
--- a/modules/field/field.api.php
+++ b/modules/field/field.api.php
@@ -124,6 +124,10 @@ function hook_field_extra_fields_alter(&$info) {
 /**
  * Define Field API field types.
  *
+ * Note that fields and their instances should never be created in the same
+ * module that defines their field type, because disabling the module will mark
+ * the fields as inactive, preventing them from being removed on uninstall.
+ *
  * @return
  *   An array whose keys are field type names and whose values are arrays
  *   describing the field type, with the following key/value pairs:
diff --git a/modules/field/field.crud.inc b/modules/field/field.crud.inc
index 339e9c4..605564a 100644
--- a/modules/field/field.crud.inc
+++ b/modules/field/field.crud.inc
@@ -23,6 +23,10 @@
  * This function does not bind the field to any bundle; use
  * field_create_instance() for that.
  *
+ * Note that fields and their instances should never be created in the same
+ * module that defines their field type, because disabling the module will mark
+ * the fields as inactive, preventing them from being removed on uninstall.
+ *
  * @param $field
  *   A field definition array. The field_name and type properties are required.
  *   Other properties, if omitted, will be given the following default values:
@@ -415,6 +419,10 @@ function field_delete_field($field_name) {
 /**
  * Creates an instance of a field, binding it to a bundle.
  *
+ * Note that fields and their instances should never be created in the same
+ * module that defines their field type, because disabling the module will mark
+ * the fields as inactive, preventing them from being removed on uninstall.
+ *
  * @param $instance
  *   A field instance definition array. The field_name, entity_type and
  *   bundle properties are required. Other properties, if omitted,
diff --git a/modules/field/field.module b/modules/field/field.module
index 9e03c8d..bc5703c 100644
--- a/modules/field/field.module
+++ b/modules/field/field.module
@@ -415,6 +415,38 @@ function field_modules_disabled($modules) {
 }
 
 /**
+ * Implements hook_system_info_alter().
+ *
+ * Goes through a list of all modules that provide a field type, and makes them
+ * required if there are any active fields of that type.
+ */
+function field_system_info_alter(&$info, $file, $type) {
+  if ($type == 'module' && module_hook($file->name, 'field_info')) {
+    $fields = field_read_fields(array('module' => $file->name));
+    if ($fields) {
+      $info['required'] = TRUE;
+
+      // Provide an explanation message (only mention pending deletions if there
+      // remains no actual, non-deleted fields)
+      $non_deleted = FALSE;
+      foreach ($fields as $field) {
+        if (empty($field['deleted'])) {
+          $non_deleted = TRUE;
+          break;
+        }
+      }
+      if ($non_deleted) {
+        $explanation = t('Field type(s) in use - see !link', array('!link' => l(t('Field list'), 'admin/reports/fields')));
+      }
+      else {
+        $explanation = t('Fields pending deletion');
+      }
+      $info['explanation'] = $explanation;
+    }
+  }
+}
+
+/**
  * Allows a module to update the database for fields and columns it controls.
  *
  * @param string $module
diff --git a/modules/field_ui/field_ui.admin.inc b/modules/field_ui/field_ui.admin.inc
index 96beb13..db31004 100644
--- a/modules/field_ui/field_ui.admin.inc
+++ b/modules/field_ui/field_ui.admin.inc
@@ -12,17 +12,27 @@ function field_ui_fields_list() {
   $instances = field_info_instances();
   $field_types = field_info_field_types();
   $bundles = field_info_bundles();
+
+  $modules = system_rebuild_module_data();
+
   $header = array(t('Field name'), t('Field type'), t('Used in'));
   $rows = array();
   foreach ($instances as $entity_type => $type_bundles) {
     foreach ($type_bundles as $bundle => $bundle_instances) {
       foreach ($bundle_instances as $field_name => $instance) {
         $field = field_info_field($field_name);
+
+        // Initialize the row if we encounter the field for the first time.
+        if (!isset($rows[$field_name])) {
+          $rows[$field_name]['class'] = $field['locked'] ? array('menu-disabled') : array('');
+          $rows[$field_name]['data'][0] = $field['locked'] ? t('@field_name (Locked)', array('@field_name' => $field_name)) : $field_name;
+          $module_name = $field_types[$field['type']]['module'];
+          $rows[$field_name]['data'][1] = $field_types[$field['type']]['label'] . ' ' . t('(module: !module)', array('!module' => $modules[$module_name]->info['name']));
+        }
+
+        // Add the current instance.
         $admin_path = _field_ui_bundle_admin_path($entity_type, $bundle);
-        $rows[$field_name]['data'][0] = $field['locked'] ? t('@field_name (Locked)', array('@field_name' => $field_name)) : $field_name;
-        $rows[$field_name]['data'][1] = $field_types[$field['type']]['label'];
         $rows[$field_name]['data'][2][] = $admin_path ? l($bundles[$entity_type][$bundle]['label'], $admin_path . '/fields') : $bundles[$entity_type][$bundle]['label'];
-        $rows[$field_name]['class'] = $field['locked'] ? array('menu-disabled') : array('');
       }
     }
   }
diff --git a/modules/system/system.admin.inc b/modules/system/system.admin.inc
index 9e7d69d..abb796c 100644
--- a/modules/system/system.admin.inc
+++ b/modules/system/system.admin.inc
@@ -799,7 +799,7 @@ function system_modules($form, $form_state = array()) {
     $extra['enabled'] = (bool) $module->status;
     if (!empty($module->info['required'] )) {
       $extra['disabled'] = TRUE;
-      $extra['required_by'][] = $distribution_name;
+      $extra['required_by'][] = $distribution_name . (!empty($module->info['explanation']) ? ' ('. $module->info['explanation'] .')' : '');
     }
 
     // If this module requires other modules, add them to the array.