diff --git a/docs/fsharp/language-reference/casting-and-conversions.md b/docs/fsharp/language-reference/casting-and-conversions.md
index 585f8ec7e91c8..26bca3f629cb7 100644
--- a/docs/fsharp/language-reference/casting-and-conversions.md
+++ b/docs/fsharp/language-reference/casting-and-conversions.md
@@ -180,7 +180,7 @@ let purchaseOrder = XElement.Load("PurchaseOrder.xml")
 let partNos = purchaseOrder.Descendants("Item")
 ```
 
-You can also optionally enable the warning 3390 (`/warnon:3390` or property `<WarnOn>3390</WarnOn>`) to show a warning at every point a .NET-style implicit conversion is used.
+You can also optionally enable the warning 3395 (`/warnon:3395` or property `<WarnOn>3395</WarnOn>`) to show a warning at every point a .NET-style implicit conversion is used.
 
 .NET-style `op_Implicit` conversions are also applied automatically for non-method-argument expressions in the same situations as implicit upcasts. However, when used widely or inappropriately, implicit conversions can interact poorly with type inference and lead to code that's harder to understand. For this reason, these always generate warnings when used in non-argument positions.
 
@@ -192,8 +192,8 @@ The following optional warnings are provided for uses of implicit conversions:
 
 * `/warnon:3388` (additional implicit upcast)
 * `/warnon:3389` (implicit numeric widening)
-* `/warnon:3390` (`op_Implicit` at method arguments)
 * `/warnon:3391` (`op_Implicit` at non-method arguments, on by default)
+* `/warnon:3395` (`op_Implicit` at method arguments)
 
 ## See also
 
diff --git a/docs/fsharp/whats-new/fsharp-6.md b/docs/fsharp/whats-new/fsharp-6.md
index d056062211413..5c37ba1baf57e 100644
--- a/docs/fsharp/whats-new/fsharp-6.md
+++ b/docs/fsharp/whats-new/fsharp-6.md
@@ -280,7 +280,10 @@ let purchaseOrder = XElement.Load("PurchaseOrder.xml")
 let partNos = purchaseOrder.Descendants("Item")
 ```
 
-You may optionally enable the warning `/warnon:3390` to show a warning at every point implicit numeric widening is used, as described in [Optional warnings for implicit conversions](#optional-warnings-for-implicit-conversions).
+You may optionally enable the warning `/warnon:3395` to show a warning at every point implicit numeric widening is used, as described in [Optional warnings for implicit conversions](#optional-warnings-for-implicit-conversions).
+
+> [!NOTE]
+> In the first release of F# 6, this warning number was `/warnon:3390`. Due to a conflict, the warning number was later updated to `/warnon:3395`.
 
 ### Optional warnings for implicit conversions
 
@@ -288,10 +291,10 @@ Type-directed and implicit conversions can interact poorly with type inference a
 
 * `/warnon:3388` (additional implicit upcast)
 * `/warnon:3389` (implicit numeric widening)
-* `/warnon:3390` (op_Implicit at method arguments)
 * `/warnon:3391` (op_Implicit at non-method arguments, on by default)
+* `/warnon:3395` (op_Implicit at method arguments)
 
-If your team wants to ban all uses of implicit conversions, you can also specify `/warnaserror:3388`, `/warnaserror:3389`, `/warnaserror:3390`, and `/warnaserror:3391`.
+If your team wants to ban all uses of implicit conversions, you can also specify `/warnaserror:3388`, `/warnaserror:3389`, `/warnaserror:3391`, and `/warnaserror:3395`.
 
 ## Formatting for binary numbers