diff --git a/lucene/tools/javadoc/ecj.javadocs.prefs b/lucene/tools/javadoc/ecj.javadocs.prefs
index bd98c99ac62..c81d8e32aa3 100644
--- a/lucene/tools/javadoc/ecj.javadocs.prefs
+++ b/lucene/tools/javadoc/ecj.javadocs.prefs
@@ -82,7 +82,7 @@ org.eclipse.jdt.core.compiler.problem.unusedDeclaredThrownException=ignore
 org.eclipse.jdt.core.compiler.problem.unusedDeclaredThrownExceptionExemptExceptionAndThrowable=enabled
 org.eclipse.jdt.core.compiler.problem.unusedDeclaredThrownExceptionIncludeDocCommentReference=enabled
 org.eclipse.jdt.core.compiler.problem.unusedDeclaredThrownExceptionWhenOverriding=disabled
-org.eclipse.jdt.core.compiler.problem.unusedImport=ignore
+org.eclipse.jdt.core.compiler.problem.unusedImport=error
 org.eclipse.jdt.core.compiler.problem.unusedLabel=ignore
 org.eclipse.jdt.core.compiler.problem.unusedLocal=ignore
 org.eclipse.jdt.core.compiler.problem.unusedObjectAllocation=ignore