diff --git a/app/changelog/page.mdx b/app/changelog/page.mdx
index 6f356f1..5b11000 100644
--- a/app/changelog/page.mdx
+++ b/app/changelog/page.mdx
@@ -18,6 +18,8 @@ This page lists changes since Working Draft 3. {{ className: 'lead' }}
 - Removed the nonce from the [signature system](/signatures), replaced with `Versia-Signed-At` (timestamps).
 - Standardize rate limits with [IETF draft draft-polli-ratelimit-headers-02](https://www.ietf.org/archive/id/draft-polli-ratelimit-headers-02.html).
 - Added [Versia Links](/links).
+- Switched from ISO 8601 to [RFC 3339](https://datatracker.ietf.org/doc/html/rfc3339) for timestamps.
+    - In most cases, the two are interchangeable, but RFC 3339 is more strict. Most implementations should not need to change anything.
 
 ## Since WD 3
 
diff --git a/app/entities/page.mdx b/app/entities/page.mdx
index 2bad0d5..ab6d22c 100644
--- a/app/entities/page.mdx
+++ b/app/entities/page.mdx
@@ -24,8 +24,8 @@ Any field in an entity not marked as `required` may be omitted or set to `null`.
         <Property name="type" type="string" required={true}>
             Type of the entity. Custom types must follow [Extension Naming](/extensions#naming).
         </Property>
-        <Property name="created_at" type="ISO8601" required={true} typeLink="/types#iso-8601">
-            Date and time when the entity was created. Must be an [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601) formatted string.
+        <Property name="created_at" type="RFC3339" required={true} typeLink="/types#rfc3339">
+            Date and time when the entity was created. Must be an [RFC 3339](https://datatracker.ietf.org/doc/html/rfc3339) timestamp.
 
             <Note>
             Handling of dates that are valid but obviously incorrect (e.g. in the future) is left to the Implementation's discretion.
diff --git a/app/extensions/polls/page.mdx b/app/extensions/polls/page.mdx
index dc048d2..e7be043 100644
--- a/app/extensions/polls/page.mdx
+++ b/app/extensions/polls/page.mdx
@@ -29,8 +29,8 @@ Note that there is no `question` field: the question should be included in the `
             <Property name="multiple_choice" type="boolean" required="true">
                 Whether the poll allows multiple votes to be cast for different options.
             </Property>
-            <Property name="expires_at" type="ISO 8601" typeLink="/types#iso8601">
-                ISO 8601 timestamp of when the poll ends and no more votes can be cast. If not present, the poll does not expire.
+            <Property name="expires_at" type="RFC3339" typeLink="/types#rfc3339">
+                RFC 3339 timestamp of when the poll ends and no more votes can be cast. If not present, the poll does not expire.
             </Property>
         </Properties>
     </Col>
diff --git a/app/extensions/vanity/page.mdx b/app/extensions/vanity/page.mdx
index 3b6d3bb..c6da43f 100644
--- a/app/extensions/vanity/page.mdx
+++ b/app/extensions/vanity/page.mdx
@@ -61,7 +61,7 @@ All properties are optional.
                 type LanguageCode = string;
                 ```
             </Property>
-            <Property name="birthday" type="ISO8601" required={false} typeLink="/types#iso8601">
+            <Property name="birthday" type="RFC3339" required={false} typeLink="/types#rfc3339">
                 User's birthday. If year is left out or set to `0000`, implementations **SHOULD** not display the year.
             </Property>
             <Property name="location" type="string" required={false}>
diff --git a/app/federation/validation/page.mdx b/app/federation/validation/page.mdx
index a980085..493b04b 100644
--- a/app/federation/validation/page.mdx
+++ b/app/federation/validation/page.mdx
@@ -17,7 +17,7 @@ Implementations **MUST** strictly validate all incoming data to ensure that it i
 Things that should be validated include, but are not limited to:
 
 - The presence of **all required fields**.
-- The **format** of all fields (integers should not be strings, dates should be in ISO 8601 format, etc.).
+- The **format** of all fields (integers should not be strings, timestamps should be in RFC 3339 format, etc.).
 - The presence of **all required headers**.
 - The presence of a **valid signature**.
 - The **length** of all fields (for example, the `username` field on a `User` entity) should be at least 1 character long.
diff --git a/app/types/page.mdx b/app/types/page.mdx
index bdf4524..d35e6fa 100644
--- a/app/types/page.mdx
+++ b/app/types/page.mdx
@@ -1,23 +1,7 @@
 
-## ISO8601
+## RFC3339
 
-```typescript
-type Year = `${number}${number}${number}${number}`;
-type Month = `${"0" | "1"}${number}`;
-type Day = `${"0" | "1" | "2" | "3"}${number}`;
-
-type DateString = `${Year}-${Month}-${Day}`;
-
-type Hour = `${"0" | "1" | "2"}${number}`;
-type Minute = `${"0" | "1" | "2" | "3" | "4" | "5"}${number}`;
-type Second = `${"0" | "1" | "2" | "3" | "4" | "5"}${number}`;
-
-type TimeString = `${Hour}:${Minute}:${Second}`;
-
-type Offset = `${"Z" | "+" | "-"}${Hour}:${Minute}`;
-
-type ISO8601 = `${DateString}T${TimeString}${Offset}`;
-```
+[https://datatracker.ietf.org/doc/html/rfc3339](https://datatracker.ietf.org/doc/html/rfc3339)
 
 ## UUID