diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 4a55c219cb6..23b89ddf75f 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -84,42 +84,59 @@ static bool isEscapeSource(const Value *V) {
 
 /// getObjectSize - Return the size of the object specified by V, or
 /// UnknownSize if unknown.
-static uint64_t getObjectSize(const Value *V, const TargetData &TD) {
+static uint64_t getObjectSize(const Value *V, const TargetData &TD,
+                              bool RoundToAlign = false) {
   Type *AccessTy;
+  unsigned Align;
   if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
     if (!GV->hasDefinitiveInitializer())
       return AliasAnalysis::UnknownSize;
     AccessTy = GV->getType()->getElementType();
+    Align = GV->getAlignment();
   } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
     if (!AI->isArrayAllocation())
       AccessTy = AI->getType()->getElementType();
     else
       return AliasAnalysis::UnknownSize;
+    Align = AI->getAlignment();
   } else if (const CallInst* CI = extractMallocCall(V)) {
-    if (!isArrayMalloc(V, &TD))
+    if (!RoundToAlign && !isArrayMalloc(V, &TD))
       // The size is the argument to the malloc call.
       if (const ConstantInt* C = dyn_cast<ConstantInt>(CI->getArgOperand(0)))
         return C->getZExtValue();
     return AliasAnalysis::UnknownSize;
   } else if (const Argument *A = dyn_cast<Argument>(V)) {
-    if (A->hasByValAttr())
+    if (A->hasByValAttr()) {
       AccessTy = cast<PointerType>(A->getType())->getElementType();
-    else
+      Align = A->getParamAlignment();
+    } else {
       return AliasAnalysis::UnknownSize;
+    }
   } else {
     return AliasAnalysis::UnknownSize;
   }
-  
-  if (AccessTy->isSized())
-    return TD.getTypeAllocSize(AccessTy);
-  return AliasAnalysis::UnknownSize;
+
+  if (!AccessTy->isSized())
+    return AliasAnalysis::UnknownSize;
+
+  uint64_t Size = TD.getTypeAllocSize(AccessTy);
+  if (RoundToAlign) {
+    if (!Align)
+      return AliasAnalysis::UnknownSize;
+    Size = RoundUpToAlignment(Size, Align);
+  }
+
+  return Size;
 }
 
 /// isObjectSmallerThan - Return true if we can prove that the object specified
 /// by V is smaller than Size.
 static bool isObjectSmallerThan(const Value *V, uint64_t Size,
                                 const TargetData &TD) {
-  uint64_t ObjectSize = getObjectSize(V, TD);
+  // This function needs to use the aligned object size because we allow
+  // reads a bit past the end given sufficient alignment.
+  uint64_t ObjectSize = getObjectSize(V, TD, /*RoundToAlign*/true);
+  
   return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size;
 }
 
diff --git a/test/Analysis/BasicAA/aligned-overread.ll b/test/Analysis/BasicAA/aligned-overread.ll
new file mode 100644
index 00000000000..b05f8eb6948
--- /dev/null
+++ b/test/Analysis/BasicAA/aligned-overread.ll
@@ -0,0 +1,25 @@
+; RUN: opt < %s -basicaa -dse -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.8.0"
+
+%struct.S0 = type <{ i8, [4 x i8] }>
+
+@a = global { i8, i8, i8, i8, i8 } { i8 undef, i8 0, i8 0, i8 0, i8 0 }, align 8
+
+define i32 @main() nounwind uwtable ssp {
+entry:
+  %tmp = load i8* getelementptr inbounds ({ i8, i8, i8, i8, i8 }* @a, i64 0, i32 4), align 4
+  %tmp1 = or i8 %tmp, -128
+  store i8 %tmp1, i8* getelementptr inbounds ({ i8, i8, i8, i8, i8 }* @a, i64 0, i32 4), align 4
+  %tmp2 = load i64* bitcast ({ i8, i8, i8, i8, i8 }* @a to i64*), align 8
+  store i8 11, i8* getelementptr inbounds ({ i8, i8, i8, i8, i8 }* @a, i64 0, i32 4), align 4
+  %tmp3 = trunc i64 %tmp2 to i32
+  ret i32 %tmp3
+
+; Make sure we don't delete either store here
+; CHECK: @main
+; CHECK: store i8 %tmp1
+; CHECK: store i8 11
+}
+
diff --git a/test/Analysis/BasicAA/global-size.ll b/test/Analysis/BasicAA/global-size.ll
index a7e5aab6c1f..617f4c3d9db 100644
--- a/test/Analysis/BasicAA/global-size.ll
+++ b/test/Analysis/BasicAA/global-size.ll
@@ -4,7 +4,7 @@
 ; RUN: opt < %s -basicaa -gvn -S | FileCheck %s
 target datalayout = "E-p:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128"
 
-@B = global i16 8
+@B = global i16 8, align 2
 
 ; CHECK: @test1
 define i16 @test1(i32* %P) {