Index: llvm/include/llvm/Bitstream/BitstreamReader.h
===================================================================
--- llvm/include/llvm/Bitstream/BitstreamReader.h
+++ llvm/include/llvm/Bitstream/BitstreamReader.h
@@ -229,21 +229,33 @@
     return R;
   }
 
-  Expected<uint32_t> ReadVBR(unsigned NumBits) {
+  Expected<uint32_t> ReadVBR(const unsigned NumBits) {
     Expected<unsigned> MaybeRead = Read(NumBits);
     if (!MaybeRead)
       return MaybeRead;
     uint32_t Piece = MaybeRead.get();
 
-    if ((Piece & (1U << (NumBits-1))) == 0)
+    if (NumBits >= 33 || NumBits == 0)
+      return make_error<StringError>("Invalid NumBits value",
+                                     llvm::inconvertibleErrorCode());
+    const uint32_t MaskBitOrder = (NumBits - 1);
+    const uint32_t Mask = 1UL << MaskBitOrder;
+
+    if ((Piece & Mask) == 0)
       return Piece;
 
     uint32_t Result = 0;
     unsigned NextBit = 0;
     while (true) {
-      Result |= (Piece & ((1U << (NumBits-1))-1)) << NextBit;
+      if (Mask > 1) {
+        if (MaskBitOrder - 1 + NextBit >= 32) {
+          return make_error<StringError>("Invalid NumBits or NextBit value",
+                                         llvm::inconvertibleErrorCode());
+        }
+      }
+      Result |= (Piece & (Mask - 1)) << NextBit;
 
-      if ((Piece & (1U << (NumBits-1))) == 0)
+      if ((Piece & Mask) == 0)
         return Result;
 
       NextBit += NumBits-1;
Index: llvm/test/Bitcode/invalid-no-ubsan.test
===================================================================
--- llvm/test/Bitcode/invalid-no-ubsan.test
+++ llvm/test/Bitcode/invalid-no-ubsan.test
@@ -6,14 +6,12 @@
 # TODO: This code should be fixed to not exhibit UB, and these tests should be
 # incorporated back into invalid.test and run under UBSan again.
 
-UNSUPPORTED: ubsan
-
 RUN: not llvm-dis -disable-output %p/Inputs/size-not-plausible.bc 2>&1 | \
 RUN:   FileCheck --check-prefix=SIZE-NOT-PLAUSIBLE %s
 
-SIZE-NOT-PLAUSIBLE: Size is not plausible
+SIZE-NOT-PLAUSIBLE: Invalid NumBits or NextBit value
 
 RUN: not llvm-dis -disable-output %p/Inputs/invalid-value-symbol-table-2.bc 2>&1 | \
 RUN:   FileCheck --check-prefix=INVALID-VALUE-SYMBOL-TABLE-2 %s
 
-INVALID-VALUE-SYMBOL-TABLE-2: Expected value symbol table subbloc
+INVALID-VALUE-SYMBOL-TABLE-2: Invalid NumBits or NextBit value