diff --git a/platform/util/src/com/intellij/openapi/util/RecursionGuard.java b/platform/util/src/com/intellij/openapi/util/RecursionGuard.java
index 9df4e10fdb7e..b016892de051 100644
--- a/platform/util/src/com/intellij/openapi/util/RecursionGuard.java
+++ b/platform/util/src/com/intellij/openapi/util/RecursionGuard.java
@@ -85,7 +85,7 @@ public abstract class RecursionGuard {
    *
    * @param since the id of a computation whose result is safe to cache whilst for more nested ones it's not.
    */
-  public abstract void prohibitResultCaching(Object since);
+  public abstract void prohibitResultCaching(@NotNull Object since);
 
   public interface StackStamp {
 
diff --git a/platform/util/src/com/intellij/openapi/util/RecursionManager.java b/platform/util/src/com/intellij/openapi/util/RecursionManager.java
index 47d32a1389f5..b40d0bb7318e 100644
--- a/platform/util/src/com/intellij/openapi/util/RecursionManager.java
+++ b/platform/util/src/com/intellij/openapi/util/RecursionManager.java
@@ -156,7 +156,7 @@ public class RecursionManager {
       }
 
       @Override
-      public void prohibitResultCaching(Object since) {
+      public void prohibitResultCaching(@NotNull Object since) {
         MyKey realKey = new MyKey(id, since, false);
         final CalculationStack stack = ourStack.get();
         stack.enableMemoization(realKey, stack.prohibitResultCaching(realKey));