diff --git a/lib/Bytecode/Reader/InstructionReader.cpp b/lib/Bytecode/Reader/InstructionReader.cpp
index 58f2656..1f4aa68 100644
--- a/lib/Bytecode/Reader/InstructionReader.cpp
+++ b/lib/Bytecode/Reader/InstructionReader.cpp
@@ -48,6 +48,7 @@
     if (read_vbr(Buf, EndBuf, Result.Opcode)) return failure(true);
     if (read_vbr(Buf, EndBuf, Typ)) return failure(true);
     Result.Ty = getType(Typ);
+    if (Result.Ty == 0) return failure(true);
     if (read_vbr(Buf, EndBuf, Result.NumOperands)) return failure(true);
 
     switch (Result.NumOperands) {
@@ -109,10 +110,13 @@
 
   Value *V;
   switch (Raw.Opcode) {
-  case Instruction::Cast:
-    Res = new CastInst(getValue(Raw.Ty, Raw.Arg1), getType(Raw.Arg2));
+  case Instruction::Cast: {
+    V = getValue(Raw.Ty, Raw.Arg1);
+    const Type *Ty = getType(Raw.Arg2);
+    if (V == 0 || Ty == 0) { cerr << "Invalid cast!\n"; return true; }
+    Res = new CastInst(V, Ty);
     return false;
-
+  }
   case Instruction::PHINode: {
     PHINode *PN = new PHINode(Raw.Ty);
     switch (Raw.NumOperands) {
diff --git a/lib/Bytecode/Writer/InstructionWriter.cpp b/lib/Bytecode/Writer/InstructionWriter.cpp
index c972a7c..c6a32ed 100644
--- a/lib/Bytecode/Writer/InstructionWriter.cpp
+++ b/lib/Bytecode/Writer/InstructionWriter.cpp
@@ -34,13 +34,20 @@
   output_vbr(Type, Out);                         // Result type
 
   unsigned NumArgs = I->getNumOperands();
-  output_vbr(NumArgs, Out);
+  output_vbr(NumArgs + isa<CastInst>(I), Out);
 
   for (unsigned i = 0; i < NumArgs; ++i) {
     int Slot = Table.getValSlot(I->getOperand(i));
     assert(Slot >= 0 && "No slot number for value!?!?");      
     output_vbr((unsigned)Slot, Out);
   }
+
+  if (isa<CastInst>(I)) {
+    int Slot = Table.getValSlot(I->getType());
+    assert(Slot != -1 && "Cast return type unknown?");
+    output_vbr((unsigned)Slot, Out);
+  }
+
   align32(Out);    // We must maintain correct alignment!
 }
 
@@ -210,7 +217,7 @@
   if (Slot > MaxOpSlot) MaxOpSlot = Slot;
 
   // Handle the special case for cast...
-  if (I->getOpcode() == Instruction::Cast) {
+  if (isa<CastInst>(I)) {
     // Cast has to encode the destination type as the second argument in the
     // packet, or else we won't know what type to cast to!
     Slots[1] = Table.getValSlot(I->getType());