diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters1.java b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters1.java
index 178492bbead..9a83e7f5063 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters1.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters1.java
@@ -16,14 +16,11 @@
 
 package org.jetbrains.jet.lang.diagnostics;
 
-import com.intellij.openapi.util.TextRange;
 import com.intellij.psi.PsiElement;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.List;
-
 public class DiagnosticWithParameters1<E extends PsiElement, A> extends AbstractDiagnostic<E> {
-    private A a;
+    private final A a;
 
     public DiagnosticWithParameters1(@NotNull E psiElement,
             @NotNull A a,
@@ -43,4 +40,9 @@ public class DiagnosticWithParameters1<E extends PsiElement, A> extends Abstract
     public A getA() {
         return a;
     }
+
+    @Override
+    public String toString() {
+        return "(a = " + a + ")";
+    }
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters2.java b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters2.java
index 79ecb04a5f6..4ee1f6c4c2c 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters2.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters2.java
@@ -16,15 +16,12 @@
 
 package org.jetbrains.jet.lang.diagnostics;
 
-import com.intellij.openapi.util.TextRange;
 import com.intellij.psi.PsiElement;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.List;
-
 public class DiagnosticWithParameters2<E extends PsiElement, A, B> extends AbstractDiagnostic<E> {
-    private A a;
-    private B b;
+    private final A a;
+    private final B b;
 
     public DiagnosticWithParameters2(@NotNull E psiElement,
             @NotNull A a,
@@ -51,4 +48,9 @@ public class DiagnosticWithParameters2<E extends PsiElement, A, B> extends Abstr
     public B getB() {
         return b;
     }
+
+    @Override
+    public String toString() {
+        return "(a = " + a + ", b = " + b + ")";
+    }
 }
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters3.java b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters3.java
index 33f09ee8266..454f85ec39c 100644
--- a/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters3.java
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/diagnostics/DiagnosticWithParameters3.java
@@ -16,16 +16,13 @@
 
 package org.jetbrains.jet.lang.diagnostics;
 
-import com.intellij.openapi.util.TextRange;
 import com.intellij.psi.PsiElement;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.List;
-
 public class DiagnosticWithParameters3<E extends PsiElement, A, B, C> extends AbstractDiagnostic<E> {
-    private A a;
-    private B b;
-    private C c;
+    private final A a;
+    private final B b;
+    private final C c;
 
     public DiagnosticWithParameters3(@NotNull E psiElement,
             @NotNull A a,
@@ -59,4 +56,10 @@ public class DiagnosticWithParameters3<E extends PsiElement, A, B, C> extends Ab
     public C getC() {
         return c;
     }
+
+
+    @Override
+    public String toString() {
+        return "(a = " + a + ", b = " + b + ", c = " + c + ")";
+    }
 }