diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/AbstractLazyMemberScope.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/AbstractLazyMemberScope.java
index 82cb84c932c..4635435e692 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/AbstractLazyMemberScope.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/AbstractLazyMemberScope.java
@@ -238,4 +238,10 @@ public abstract class AbstractLazyMemberScope<D extends DeclarationDescriptor, D
             result.add(receiver);
         }
     }
+
+    // Do not change this, override in concrete subclasses:
+    // it is very easy to compromise laziness of this class, and fail all the debugging
+    // a generic implementation can't do this properly
+    @Override
+    public abstract String toString();
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyClassMemberScope.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyClassMemberScope.java
index 7f75701fccf..c4ba917781b 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyClassMemberScope.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyClassMemberScope.java
@@ -202,4 +202,10 @@ public class LazyClassMemberScope extends AbstractLazyMemberScope<LazyClassDescr
             }
         }));
     }
+
+    @Override
+    public String toString() {
+        // Do not add details here, they may compromise the laziness during debugging
+        return "lazy scope for class " + thisDescriptor.getName();
+    }
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyPackageMemberScope.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyPackageMemberScope.java
index a0434abce24..cd297047cdd 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyPackageMemberScope.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/lazy/LazyPackageMemberScope.java
@@ -93,4 +93,10 @@ public class LazyPackageMemberScope extends AbstractLazyMemberScope<NamespaceDes
             getNamespace(packageFqName.shortName());
         }
     }
+
+    @Override
+    public String toString() {
+        // Do not add details here, they may compromise the laziness during debugging
+        return "lazy scope for package " + thisDescriptor.getName();
+    }
 }