diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 4fc34d6a5..a50c39076 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -9,6 +9,7 @@ Release Notes
 * Event Grid: Add ServiceBus Queue and Topic as supported destinations
 * Functions: Support for 64 bits.
 * Functions: Add option to use managed Key Vault
+* Functions: Add support for dotnet-isolated runtime (NET5)
 * KeyVault: Fix an issue with adding tags on main KeyVault builder.
 * ServiceBus: update namespace validation rules to follow [Microsoft documentation](https://docs.microsoft.com/en-us/azure/azure-resource-manager/management/resource-name-rules#microsoftservicebus)
 * Storage: Add support for tables
diff --git a/src/Farmer/Builders/Builders.Functions.fs b/src/Farmer/Builders/Builders.Functions.fs
index bdb12aa5f..e07b7f6b4 100644
--- a/src/Farmer/Builders/Builders.Functions.fs
+++ b/src/Farmer/Builders/Builders.Functions.fs
@@ -12,7 +12,7 @@ open Farmer.Arm.KeyVault
 open Farmer.Arm.KeyVault.Vaults
 open System
 
-type FunctionsRuntime = DotNet | Node | Java | Python
+type FunctionsRuntime = DotNet | DotNetIsolated | Node | Java | Python
 type FunctionsExtensionVersion = V1 | V2 | V3
 
 module private FunctionsConfig =
@@ -142,6 +142,11 @@ type FunctionsConfig =
             | None ->
                 ()
 
+            let functionsRuntime =
+                match this.Runtime with
+                | DotNetIsolated -> "dotnet-isolated"
+                | DotNet -> "dotnet"
+                | other -> (string other).ToLower()
             { Name = this.Name
               ServicePlan = this.ServicePlanId
               Location = location
@@ -149,7 +154,7 @@ type FunctionsConfig =
               Tags = this.Tags
               ConnectionStrings = Map.empty
               AppSettings = [
-                "FUNCTIONS_WORKER_RUNTIME", (string this.Runtime).ToLower()
+                "FUNCTIONS_WORKER_RUNTIME", functionsRuntime
                 "WEBSITE_NODE_DEFAULT_VERSION", "10.14.1"
                 "FUNCTIONS_EXTENSION_VERSION", match this.ExtensionVersion with V1 -> "~1" | V2 -> "~2" | V3 -> "~3"
                 "AzureWebJobsStorage", StorageAccount.getConnectionString this.StorageAccountName |> ArmExpression.Eval
diff --git a/src/Tests/Functions.fs b/src/Tests/Functions.fs
index 73d92f97c..9df21fdfd 100644
--- a/src/Tests/Functions.fs
+++ b/src/Tests/Functions.fs
@@ -106,4 +106,11 @@ let tests = testList "Functions tests" [
         Expect.equal secrets.[1].Value (ExpressionSecret sa.Key) "Incorrect secret value"
         Expect.sequenceEqual secrets.[1].Dependencies [ vaults.resourceId "testfuncvault"; storageAccounts.resourceId "teststorage" ] "Incorrect secret dependencies"
     }
+
+    test "Supports dotnet-isolated runtime" {
+        let f = functions { use_runtime (FunctionsRuntime.DotNetIsolated) }
+        let resources = (f :> IBuilder).BuildResources Location.WestEurope
+        let site = resources.[0] :?> Web.Site
+        Expect.equal site.AppSettings.["FUNCTIONS_WORKER_RUNTIME"] (LiteralSetting "dotnet-isolated") "Should use dotnet-isolated functions runtime"
+    }
 ]
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