diff --git a/Sources/Vexil/Pole.swift b/Sources/Vexil/Pole.swift
index 13b50988..e6bc779d 100644
--- a/Sources/Vexil/Pole.swift
+++ b/Sources/Vexil/Pole.swift
@@ -87,9 +87,11 @@ public final class FlagPole<RootGroup>: Sendable where RootGroup: FlagContainer
     ///
     public static var defaultSources: [any FlagValueSource] {
 #if !os(Linux)
-        [
-            FlagValueSourceCoordinator(source: UserDefaults.standard),
-        ]
+#if swift(>=6)
+        [ FlagValueSourceCoordinator(source: UserDefaults.standard) ]
+#else
+        [ FlagValueSourceCoordinator(uncheckedSource: UserDefaults.standard) ]
+#endif
 #else
         []
 #endif
diff --git a/Sources/Vexil/Sources/FlagValueSourceCoordinator.swift b/Sources/Vexil/Sources/FlagValueSourceCoordinator.swift
index 62a0584f..61e2c19e 100644
--- a/Sources/Vexil/Sources/FlagValueSourceCoordinator.swift
+++ b/Sources/Vexil/Sources/FlagValueSourceCoordinator.swift
@@ -27,10 +27,20 @@ public final class FlagValueSourceCoordinator<Source>: Sendable where Source: No
 
     // MARK: - Initialisation
 
-    public init(source: Source) {
+    /// Create a FlagValueSource from a NonSendableFlagValueSource. If `Source` is a reference type,
+    /// you must not continue to access it (except via this coordinator) after passing it to this
+    /// initializer.
+    public init(uncheckedSource source: Source) {
         self.source = .init(uncheckedState: source)
     }
 
+#if swift(>=6)
+    /// Create a FlagValueSource from a NonSendableFlagValueSource.
+    public init(source: sending Source) {
+        self.source = .init(uncheckedState: source)
+    }
+#endif
+
 }