diff --git a/compiler/backend/src/org/jetbrains/jet/codegen/GenerationState.java b/compiler/backend/src/org/jetbrains/jet/codegen/GenerationState.java
index 9fa6f574c82..9043959432e 100644
--- a/compiler/backend/src/org/jetbrains/jet/codegen/GenerationState.java
+++ b/compiler/backend/src/org/jetbrains/jet/codegen/GenerationState.java
@@ -56,6 +56,8 @@ public class GenerationState {
     private final ClassBuilderMode classBuilderMode;
 
 
+    private boolean poisoned = false;
+
     // out parameter
     private Method scriptConstructorMethod;
 
@@ -76,6 +78,13 @@ public class GenerationState {
                 this.files, project, compilerSpecialMode, builderFactory.getClassBuilderMode(), this, builderFactory);
     }
 
+    private void poison() {
+        if (poisoned) {
+            throw new IllegalStateException("already poisoned");
+        }
+        poisoned = true;
+    }
+
     @NotNull
     public ClassFileFactory getFactory() {
         return getInjector().getClassFileFactory();
@@ -128,6 +137,7 @@ public class GenerationState {
     }
 
     public void compileCorrectFiles(@NotNull CompilationErrorHandler errorHandler) {
+        poison();
 
         for (JetFile file : this.files) {
             if (file.isScript()) {