diff --git a/bramble-api/src/main/java/org/briarproject/bramble/api/nullsafety/NullSafety.java b/bramble-api/src/main/java/org/briarproject/bramble/api/nullsafety/NullSafety.java
index 8e98561ee..5ff717a96 100644
--- a/bramble-api/src/main/java/org/briarproject/bramble/api/nullsafety/NullSafety.java
+++ b/bramble-api/src/main/java/org/briarproject/bramble/api/nullsafety/NullSafety.java
@@ -22,4 +22,11 @@ public class NullSafety {
 			@Nullable Object b) {
 		if ((a == null) == (b == null)) throw new AssertionError();
 	}
+
+	/**
+	 * Checks that the argument is null.
+	 */
+	public static void requireNull(@Nullable Object o) {
+		if (o != null) throw new AssertionError();
+	}
 }