diff --git a/versions/3.1.0.md b/versions/3.1.0.md
index f0c7f54abe..0f32fcbd98 100644
--- a/versions/3.1.0.md
+++ b/versions/3.1.0.md
@@ -3165,12 +3165,12 @@ animals:
 #### <a name="securitySchemeObject"></a>Security Scheme Object
 
 Defines a security scheme that can be used by the operations.
-Supported schemes are HTTP authentication, an API key (either as a header, a cookie parameter or as a query parameter), OAuth2's common flows (implicit, password, application and access code) as defined in [RFC6749](https://tools.ietf.org/html/rfc6749), and [OpenID Connect Discovery](https://tools.ietf.org/html/draft-ietf-oauth-discovery-06).
+Supported schemes are HTTP authentication, an API key (either as a header, a cookie parameter or as a query parameter), OAuth2's common flows (implicit, password, application and access code) as defined in [RFC6749](https://tools.ietf.org/html/rfc6749), and [OpenID Connect Discovery](https://tools.ietf.org/html/draft-ietf-oauth-discovery-06). Additional "custom" schemes can be described but the level of tool support will be limited.
 
 ##### Fixed Fields
 Field Name | Type | Applies To | Description
 ---|:---:|---|---
-<a name="securitySchemeType"></a>type | `string` | Any | **REQUIRED**. The type of the security scheme. Valid values are `"apiKey"`, `"http"`, `"oauth2"`, `"openIdConnect"`.
+<a name="securitySchemeType"></a>type | `string` | Any | **REQUIRED**. The type of the security scheme. Valid values are `"apiKey"`, `"http"`, `"oauth2"`, `"openIdConnect"`, `"custom"`.
 <a name="securitySchemeDescription"></a>description | `string` | Any | A short description for security scheme. [CommonMark syntax](http://spec.commonmark.org/) MAY be used for rich text representation.
 <a name="securitySchemeName"></a>name | `string` | `apiKey` | **REQUIRED**. The name of the header, query or cookie parameter to be used.
 <a name="securitySchemeIn"></a>in | `string` | `apiKey` | **REQUIRED**. The location of the API key. Valid values are `"query"`, `"header"` or `"cookie"`.
@@ -3178,9 +3178,12 @@ Field Name | Type | Applies To | Description
 <a name="securitySchemeBearerFormat"></a>bearerFormat | `string` | `http` (`"bearer"`) | A hint to the client to identify how the bearer token is formatted.  Bearer tokens are usually generated by an authorization server, so this information is primarily for documentation purposes.
 <a name="securitySchemeFlows"></a>flows | [OAuth Flows Object](#oauthFlowsObject) | `oauth2` | **REQUIRED**. An object containing configuration information for the flow types supported.
 <a name="securitySchemeOpenIdConnectUrl"></a>openIdConnectUrl | `string` | `openIdConnect` | **REQUIRED**. OpenId Connect URL to discover OAuth2 configuration values. This MUST be in the form of a URL.
+<a name="customType"></a>extensionType | `string` | `custom` | **REQUIRED**. When the security scheme type is custom, the customType field provides an identifier for the type of custom scheme. The valid values for this field are not controlled. Use of a well known identifier or MIME Type is encouraged to avoid collisions.
 
 This object MAY be extended with [Specification Extensions](#specificationExtensions).
 
+Custom schemes may be processed in much the same manner as extensions. Validating implementations MUST accept "custom" as a valid value for the securitySchemeType field.  They MUST also validate that the customType field is present and populated when the value of securitySchemeType is "custom". Any additional data needed to describe the custom schema SHOULD be provided using [Specification Extensions](#specificationExtensions).
+
 ##### Security Scheme Object Example
 
 ###### Basic Authentication Sample