diff --git a/platform/platform-impl/src/com/intellij/ide/ui/laf/darcula/ui/TextFieldWithPopupHandlerUI.java b/platform/platform-impl/src/com/intellij/ide/ui/laf/darcula/ui/TextFieldWithPopupHandlerUI.java
index 30cb96f4c5b6..019d3f0c4422 100644
--- a/platform/platform-impl/src/com/intellij/ide/ui/laf/darcula/ui/TextFieldWithPopupHandlerUI.java
+++ b/platform/platform-impl/src/com/intellij/ide/ui/laf/darcula/ui/TextFieldWithPopupHandlerUI.java
@@ -14,6 +14,7 @@ import com.intellij.util.ui.JBUI;
 import com.intellij.util.ui.UIUtil;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.TestOnly;
 
 import javax.swing.*;
 import javax.swing.event.DocumentEvent;
@@ -236,11 +237,12 @@ public abstract class TextFieldWithPopupHandlerUI extends BasicTextFieldUI imple
     POPUP, CLEAR, NEWLINE
   }
 
+  @TestOnly
   @NotNull
   public Point getExtensionIconLocation(@NotNull final Extension extension) {
     final IconHolder iconHolder = icons.get(extension.toString());
     if (iconHolder == null) {
-      throw new IllegalArgumentException("Unknown extension");
+      throw new IllegalArgumentException("The " + extension + " extension does not exist in this text field");
     }
     return iconHolder.bounds.getLocation();
   }