diff --git a/compiler/fir/java/src/org/jetbrains/kotlin/fir/java/declarations/FirJavaClass.kt b/compiler/fir/java/src/org/jetbrains/kotlin/fir/java/declarations/FirJavaClass.kt
index 823e946098c..5e2b785337b 100644
--- a/compiler/fir/java/src/org/jetbrains/kotlin/fir/java/declarations/FirJavaClass.kt
+++ b/compiler/fir/java/src/org/jetbrains/kotlin/fir/java/declarations/FirJavaClass.kt
@@ -143,6 +143,7 @@ internal class FirJavaClassBuilder : FirRegularClassBuilder(), FirAnnotationCont
             isCompanion = false
             isData = false
             isInline = false
+            isFun = classKind == ClassKind.INTERFACE
         }
 
         return FirJavaClass(