diff --git a/lib/VMCore/Instructions.cpp b/lib/VMCore/Instructions.cpp
index af1492d356a..91f0febf349 100644
--- a/lib/VMCore/Instructions.cpp
+++ b/lib/VMCore/Instructions.cpp
@@ -2076,6 +2076,7 @@ unsigned CastInst::isEliminableCastPair(
 
 CastInst *CastInst::Create(Instruction::CastOps op, Value *S, const Type *Ty, 
   const Twine &Name, Instruction *InsertBefore) {
+  assert(castIsValid(op, S, Ty) && "Invalid cast!");
   // Construct and return the appropriate CastInst subclass
   switch (op) {
     case Trunc:    return new TruncInst    (S, Ty, Name, InsertBefore);
@@ -2098,6 +2099,7 @@ CastInst *CastInst::Create(Instruction::CastOps op, Value *S, const Type *Ty,
 
 CastInst *CastInst::Create(Instruction::CastOps op, Value *S, const Type *Ty,
   const Twine &Name, BasicBlock *InsertAtEnd) {
+  assert(castIsValid(op, S, Ty) && "Invalid cast!");
   // Construct and return the appropriate CastInst subclass
   switch (op) {
     case Trunc:    return new TruncInst    (S, Ty, Name, InsertAtEnd);
@@ -2263,8 +2265,8 @@ bool CastInst::isCastable(const Type *SrcTy, const Type *DestTy) {
       }
 
   // Get the bit sizes, we'll need these
-  unsigned SrcBits = SrcTy->getScalarSizeInBits();   // 0 for ptr
-  unsigned DestBits = DestTy->getScalarSizeInBits(); // 0 for ptr
+  unsigned SrcBits = SrcTy->getPrimitiveSizeInBits();   // 0 for ptr
+  unsigned DestBits = DestTy->getPrimitiveSizeInBits(); // 0 for ptr
 
   // Run through the possibilities ...
   if (DestTy->isIntegerTy()) {                   // Casting to integral
@@ -2348,8 +2350,8 @@ CastInst::getCastOpcode(
       }
 
   // Get the bit sizes, we'll need these
-  unsigned SrcBits = SrcTy->getScalarSizeInBits();   // 0 for ptr
-  unsigned DestBits = DestTy->getScalarSizeInBits(); // 0 for ptr
+  unsigned SrcBits = SrcTy->getPrimitiveSizeInBits();   // 0 for ptr
+  unsigned DestBits = DestTy->getPrimitiveSizeInBits(); // 0 for ptr
 
   // Run through the possibilities ...
   if (DestTy->isIntegerTy()) {                      // Casting to integral
@@ -2463,46 +2465,40 @@ CastInst::castIsValid(Instruction::CastOps op, Value *S, const Type *DstTy) {
   unsigned SrcBitSize = SrcTy->getScalarSizeInBits();
   unsigned DstBitSize = DstTy->getScalarSizeInBits();
 
+  // If these are vector types, get the lengths of the vectors (using zero for
+  // scalar types means that checking that vector lengths match also checks that
+  // scalars are not being converted to vectors or vectors to scalars).
+  unsigned SrcLength = SrcTy->isVectorTy() ?
+    cast<VectorType>(SrcTy)->getNumElements() : 0;
+  unsigned DstLength = DstTy->isVectorTy() ?
+    cast<VectorType>(DstTy)->getNumElements() : 0;
+
   // Switch on the opcode provided
   switch (op) {
   default: return false; // This is an input error
   case Instruction::Trunc:
-    return SrcTy->isIntOrIntVectorTy() &&
-           DstTy->isIntOrIntVectorTy()&& SrcBitSize > DstBitSize;
+    return SrcTy->isIntOrIntVectorTy() && DstTy->isIntOrIntVectorTy() &&
+      SrcLength == DstLength && SrcBitSize > DstBitSize;
   case Instruction::ZExt:
-    return SrcTy->isIntOrIntVectorTy() &&
-           DstTy->isIntOrIntVectorTy()&& SrcBitSize < DstBitSize;
+    return SrcTy->isIntOrIntVectorTy() && DstTy->isIntOrIntVectorTy() &&
+      SrcLength == DstLength && SrcBitSize < DstBitSize;
   case Instruction::SExt: 
-    return SrcTy->isIntOrIntVectorTy() &&
-           DstTy->isIntOrIntVectorTy()&& SrcBitSize < DstBitSize;
+    return SrcTy->isIntOrIntVectorTy() && DstTy->isIntOrIntVectorTy() &&
+      SrcLength == DstLength && SrcBitSize < DstBitSize;
   case Instruction::FPTrunc:
-    return SrcTy->isFPOrFPVectorTy() &&
-           DstTy->isFPOrFPVectorTy() && 
-           SrcBitSize > DstBitSize;
+    return SrcTy->isFPOrFPVectorTy() && DstTy->isFPOrFPVectorTy() &&
+      SrcLength == DstLength && SrcBitSize > DstBitSize;
   case Instruction::FPExt:
-    return SrcTy->isFPOrFPVectorTy() &&
-           DstTy->isFPOrFPVectorTy() && 
-           SrcBitSize < DstBitSize;
+    return SrcTy->isFPOrFPVectorTy() && DstTy->isFPOrFPVectorTy() &&
+      SrcLength == DstLength && SrcBitSize < DstBitSize;
   case Instruction::UIToFP:
   case Instruction::SIToFP:
-    if (const VectorType *SVTy = dyn_cast<VectorType>(SrcTy)) {
-      if (const VectorType *DVTy = dyn_cast<VectorType>(DstTy)) {
-        return SVTy->getElementType()->isIntOrIntVectorTy() &&
-               DVTy->getElementType()->isFPOrFPVectorTy() &&
-               SVTy->getNumElements() == DVTy->getNumElements();
-      }
-    }
-    return SrcTy->isIntOrIntVectorTy() && DstTy->isFPOrFPVectorTy();
+    return SrcTy->isIntOrIntVectorTy() && DstTy->isFPOrFPVectorTy() &&
+      SrcLength == DstLength;
   case Instruction::FPToUI:
   case Instruction::FPToSI:
-    if (const VectorType *SVTy = dyn_cast<VectorType>(SrcTy)) {
-      if (const VectorType *DVTy = dyn_cast<VectorType>(DstTy)) {
-        return SVTy->getElementType()->isFPOrFPVectorTy() &&
-               DVTy->getElementType()->isIntOrIntVectorTy() &&
-               SVTy->getNumElements() == DVTy->getNumElements();
-      }
-    }
-    return SrcTy->isFPOrFPVectorTy() && DstTy->isIntOrIntVectorTy();
+    return SrcTy->isFPOrFPVectorTy() && DstTy->isIntOrIntVectorTy() &&
+      SrcLength == DstLength;
   case Instruction::PtrToInt:
     return SrcTy->isPointerTy() && DstTy->isIntegerTy();
   case Instruction::IntToPtr:
diff --git a/test/Assembler/invalid_cast.ll b/test/Assembler/invalid_cast.ll
new file mode 100644
index 00000000000..c5b082b6b8d
--- /dev/null
+++ b/test/Assembler/invalid_cast.ll
@@ -0,0 +1,6 @@
+; RUN: not llvm-as < %s |& grep {invalid cast opcode}
+
+define <3 x i8> @foo(<4 x i64> %x) {
+  %y = trunc <4 x i64> %x to <3 x i8>
+  ret <3 x i8> %y
+}
diff --git a/test/Assembler/invalid_cast2.ll b/test/Assembler/invalid_cast2.ll
new file mode 100644
index 00000000000..f2e7c414e71
--- /dev/null
+++ b/test/Assembler/invalid_cast2.ll
@@ -0,0 +1,6 @@
+; RUN: not llvm-as < %s |& grep {invalid cast opcode}
+
+define i8 @foo(<4 x i64> %x) {
+  %y = trunc <4 x i64> %x to i8
+  ret i8 %y
+}