diff --git a/src/main/java/de/dhbwstuttgart/bytecode/Codegen.java b/src/main/java/de/dhbwstuttgart/bytecode/Codegen.java
index 77d1460c..d5b11caa 100644
--- a/src/main/java/de/dhbwstuttgart/bytecode/Codegen.java
+++ b/src/main/java/de/dhbwstuttgart/bytecode/Codegen.java
@@ -305,8 +305,11 @@ public class Codegen {
 
     private boolean isFunctionalInterface(TargetType type) {
         if (type instanceof TargetFunNType) return true;
-        if (type instanceof TargetRefType)
-            return compiler.getClass(new JavaClassName(type.name())).isFunctionalInterface();
+        if (type instanceof TargetRefType) {
+            var clazz = compiler.getClass(new JavaClassName(type.name()));
+            return (clazz.getModifiers() & Modifier.INTERFACE) != 0 && clazz.isFunctionalInterface();
+        }
+
         return false;
     }