Index: llvm/trunk/lib/Bitcode/Reader/BitstreamReader.cpp
===================================================================
--- llvm/trunk/lib/Bitcode/Reader/BitstreamReader.cpp
+++ llvm/trunk/lib/Bitcode/Reader/BitstreamReader.cpp
@@ -319,9 +319,9 @@
 }
 
 bool BitstreamCursor::ReadBlockInfoBlock() {
-  // If this is the second stream to get to the block info block, skip it.
+  // We expect the client to read the block info block at most once.
   if (getBitStreamReader()->hasBlockInfoRecords())
-    return SkipBlock();
+    report_fatal_error("Duplicate read of block info block");
 
   if (EnterSubBlock(bitc::BLOCKINFO_BLOCK_ID)) return true;