diff --git a/include/llvm/Instructions.h b/include/llvm/Instructions.h
index 273c9951c62..118a42d5153 100644
--- a/include/llvm/Instructions.h
+++ b/include/llvm/Instructions.h
@@ -31,6 +31,10 @@ class APInt;
 class LLVMContext;
 class DominatorTree;
 
+/// MaximumAlignment - This is the greatest alignment value supported by
+/// load, store, and alloca instructions.
+static const unsigned MaximumAlignment = 1u << 29;
+
 //===----------------------------------------------------------------------===//
 //                                AllocaInst Class
 //===----------------------------------------------------------------------===//
diff --git a/lib/AsmParser/LLParser.cpp b/lib/AsmParser/LLParser.cpp
index 61b1ae5e97c..e581a694586 100644
--- a/lib/AsmParser/LLParser.cpp
+++ b/lib/AsmParser/LLParser.cpp
@@ -1154,6 +1154,8 @@ bool LLParser::ParseOptionalAlignment(unsigned &Alignment) {
   if (ParseUInt32(Alignment)) return true;
   if (!isPowerOf2_32(Alignment))
     return Error(AlignLoc, "alignment is not a power of two");
+  if (Alignment > MaximumAlignment)
+    return Error(AlignLoc, "huge alignments are not supported yet");
   return false;
 }
 
@@ -1176,6 +1178,7 @@ bool LLParser::ParseOptionalCommaAlign(unsigned &Alignment,
     if (Lex.getKind() != lltok::kw_align)
       return Error(Lex.getLoc(), "expected metadata or 'align'");
     
+    LocTy AlignLoc = Lex.getLoc();
     if (ParseOptionalAlignment(Alignment)) return true;
   }
 
diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 0d5e30205a0..fdb2dd693d9 100644
--- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -104,11 +104,15 @@ unsigned InstCombiner::GetOrEnforceKnownAlignment(Value *V,
   ComputeMaskedBits(V, Mask, KnownZero, KnownOne);
   unsigned TrailZ = KnownZero.countTrailingOnes();
 
-  // LLVM doesn't support alignments larger than this currently.
+  // Avoid trouble with rediculously large TrailZ values, such as
+  // those computed from a null pointer.
   TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
 
   unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
 
+  // LLVM doesn't support alignments larger than this currently.
+  Align = std::min(Align, MaximumAlignment);
+
   if (PrefAlign > Align)
     Align = EnforceKnownAlignment(V, Align, PrefAlign);
   
diff --git a/lib/VMCore/Instructions.cpp b/lib/VMCore/Instructions.cpp
index 57b7f3f3d64..e03cc827580 100644
--- a/lib/VMCore/Instructions.cpp
+++ b/lib/VMCore/Instructions.cpp
@@ -891,6 +891,8 @@ AllocaInst::~AllocaInst() {
 
 void AllocaInst::setAlignment(unsigned Align) {
   assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
+  assert(Align <= MaximumAlignment &&
+         "Alignment is greater than MaximumAlignment!");
   setInstructionSubclassData(Log2_32(Align) + 1);
   assert(getAlignment() == Align && "Alignment representation error!");
 }
@@ -1026,8 +1028,11 @@ LoadInst::LoadInst(Value *Ptr, const char *Name, bool isVolatile,
 
 void LoadInst::setAlignment(unsigned Align) {
   assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
+  assert(Align <= MaximumAlignment &&
+         "Alignment is greater than MaximumAlignment!");
   setInstructionSubclassData((getSubclassDataFromInstruction() & 1) |
                              ((Log2_32(Align)+1)<<1));
+  assert(getAlignment() == Align && "Alignment representation error!");
 }
 
 //===----------------------------------------------------------------------===//
@@ -1122,8 +1127,11 @@ StoreInst::StoreInst(Value *val, Value *addr, bool isVolatile,
 
 void StoreInst::setAlignment(unsigned Align) {
   assert((Align & (Align-1)) == 0 && "Alignment is not a power of 2!");
+  assert(Align <= MaximumAlignment &&
+         "Alignment is greater than MaximumAlignment!");
   setInstructionSubclassData((getSubclassDataFromInstruction() & 1) |
                              ((Log2_32(Align)+1) << 1));
+  assert(getAlignment() == Align && "Alignment representation error!");
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/test/Assembler/align-inst-alloca.ll b/test/Assembler/align-inst-alloca.ll
new file mode 100644
index 00000000000..0343bebf187
--- /dev/null
+++ b/test/Assembler/align-inst-alloca.ll
@@ -0,0 +1,6 @@
+; RUN: not llvm-as %s -o /dev/null 2>/dev/null
+
+define void @foo() {
+  %p = alloca i1, align 1073741824
+  ret void
+}
diff --git a/test/Assembler/align-inst-load.ll b/test/Assembler/align-inst-load.ll
new file mode 100644
index 00000000000..3586be2d6e0
--- /dev/null
+++ b/test/Assembler/align-inst-load.ll
@@ -0,0 +1,6 @@
+; RUN: not llvm-as %s -o /dev/null 2>/dev/null
+
+define void @foo() {
+  load i1* %p, align 1073741824
+  ret void
+}
diff --git a/test/Assembler/align-inst-store.ll b/test/Assembler/align-inst-store.ll
new file mode 100644
index 00000000000..8c3b7124b43
--- /dev/null
+++ b/test/Assembler/align-inst-store.ll
@@ -0,0 +1,6 @@
+; RUN: not llvm-as %s -o /dev/null 2>/dev/null
+
+define void @foo() {
+  store i1 false, i1* %p, align 1073741824
+  ret void
+}
diff --git a/test/Assembler/align-inst.ll b/test/Assembler/align-inst.ll
new file mode 100644
index 00000000000..7bf0b6493b6
--- /dev/null
+++ b/test/Assembler/align-inst.ll
@@ -0,0 +1,8 @@
+; RUN: llvm-as %s -o /dev/null
+
+define void @foo() {
+  %p = alloca i1, align 536870912
+  load i1* %p, align 536870912
+  store i1 false, i1* %p, align 536870912
+  ret void
+}