diff --git a/platform/analysis-impl/src/com/intellij/codeInsight/completion/CompletionInitializationUtil.java b/platform/analysis-impl/src/com/intellij/codeInsight/completion/CompletionInitializationUtil.java
index 85f2404b0d83..f8904a2f9558 100644
--- a/platform/analysis-impl/src/com/intellij/codeInsight/completion/CompletionInitializationUtil.java
+++ b/platform/analysis-impl/src/com/intellij/codeInsight/completion/CompletionInitializationUtil.java
@@ -24,6 +24,7 @@ import com.intellij.psi.impl.PsiFileEx;
 import com.intellij.psi.impl.source.PsiFileImpl;
 import com.intellij.psi.util.PsiTreeUtil;
 import com.intellij.psi.util.PsiUtilBase;
+import com.intellij.psi.util.PsiUtilCore;
 import com.intellij.reference.SoftReference;
 import org.jetbrains.annotations.ApiStatus;
 import org.jetbrains.annotations.NotNull;
@@ -140,7 +141,7 @@ public class CompletionInitializationUtil {
       if (originalFile != injected &&
           injected instanceof PsiFileImpl &&
           InjectedLanguageManager.getInstance(originalFile.getProject()).isInjectedFragment(originalFile)) {
-        ((PsiFileImpl)injected).setOriginalFile(originalFile);
+        setOriginalFile((PsiFileImpl)injected, originalFile);
       }
       VirtualFile virtualFile = injected.getVirtualFile();
       DocumentWindow documentWindow = null;
@@ -157,6 +158,16 @@ public class CompletionInitializationUtil {
     return hostCopyOffsets;
   }
 
+  private static void setOriginalFile(PsiFileImpl copy, PsiFile origin) {
+    PsiFile currentOrigin = copy.getOriginalFile();
+    if (currentOrigin == copy) {
+      copy.setOriginalFile(origin);
+    } else {
+      PsiUtilCore.ensureValid(currentOrigin);
+      LOG.assertTrue(currentOrigin == origin);
+    }
+  }
+
   @NotNull
   private static PsiElement findCompletionPositionLeaf(OffsetsInFile offsets, int offset, PsiFile originalFile) {
     PsiElement insertedElement = offsets.getFile().findElementAt(offset);