diff --git a/lib/Target/TargetData.cpp b/lib/Target/TargetData.cpp
index bd6a6b6..ff60e0b 100644
--- a/lib/Target/TargetData.cpp
+++ b/lib/Target/TargetData.cpp
@@ -125,15 +125,15 @@
 //===----------------------------------------------------------------------===//
 
 /// getInt - Get an integer ignoring errors.
-static unsigned getInt(StringRef R) {
-  unsigned Result = 0;
+static int getInt(StringRef R) {
+  int Result = 0;
   R.getAsInteger(10, Result);
   return Result;
 }
 
-void TargetData::init(StringRef Desc) {
+void TargetData::init() {
   initializeTargetDataPass(*PassRegistry::getPassRegistry());
-  
+
   LayoutMap = 0;
   LittleEndian = false;
   PointerMemSize = 8;
@@ -152,6 +152,12 @@
   setAlignment(VECTOR_ALIGN,    8,  8, 64);  // v2i32, v1i64, ...
   setAlignment(VECTOR_ALIGN,   16, 16, 128); // v16i8, v8i16, v4i32, ...
   setAlignment(AGGREGATE_ALIGN, 0,  8,  0);  // struct
+}
+
+std::string TargetData::parseSpecifier(StringRef Desc, TargetData *td) {
+
+  if (td)
+    td->init();
 
   while (!Desc.empty()) {
     std::pair<StringRef, StringRef> Split = Desc.split('-');
@@ -169,28 +175,54 @@
 
     switch (Specifier[0]) {
     case 'E':
-      LittleEndian = false;
+      if (td)
+        td->LittleEndian = false;
       break;
     case 'e':
-      LittleEndian = true;
+      if (td)
+        td->LittleEndian = true;
       break;
-    case 'p':
+    case 'p': {
+      // Pointer size.
       Split = Token.split(':');
-      PointerMemSize = getInt(Split.first) / 8;
+      int PointerMemSizeBits = getInt(Split.first);
+      if (PointerMemSizeBits < 0 || PointerMemSizeBits % 8 != 0)
+        return "invalid pointer size, must be a positive 8-bit multiple";
+      if (td)
+        td->PointerMemSize = PointerMemSizeBits / 8;
+
+      // Pointer ABI alignment.
       Split = Split.second.split(':');
-      PointerABIAlign = getInt(Split.first) / 8;
+      int PointerABIAlignBits = getInt(Split.first);
+      if (PointerABIAlignBits < 0 || PointerABIAlignBits % 8 != 0) {
+        return "invalid pointer ABI alignment, "
+               "must be a positive 8-bit multiple";
+      }
+      if (td)
+        td->PointerABIAlign = PointerABIAlignBits / 8;
+
+      // Pointer preferred alignment.
       Split = Split.second.split(':');
-      PointerPrefAlign = getInt(Split.first) / 8;
-      if (PointerPrefAlign == 0)
-        PointerPrefAlign = PointerABIAlign;
+      int PointerPrefAlignBits = getInt(Split.first);
+      if (PointerPrefAlignBits < 0 || PointerPrefAlignBits % 8 != 0) {
+        return "invalid pointer preferred alignment, "
+               "must be a positive 8-bit multiple";
+      }
+      if (td) {
+        td->PointerPrefAlign = PointerPrefAlignBits / 8;
+        if (td->PointerPrefAlign == 0)
+          td->PointerPrefAlign = td->PointerABIAlign;
+      }
       break;
+    }
     case 'i':
     case 'v':
     case 'f':
     case 'a':
     case 's': {
       AlignTypeEnum AlignType;
-      switch (Specifier[0]) {
+      char field = Specifier[0];
+      switch (field) {
       default:
       case 'i': AlignType = INTEGER_ALIGN; break;
       case 'v': AlignType = VECTOR_ALIGN; break;
@@ -198,37 +230,66 @@
       case 'a': AlignType = AGGREGATE_ALIGN; break;
       case 's': AlignType = STACK_ALIGN; break;
       }
-      unsigned Size = getInt(Specifier.substr(1));
+      int Size = getInt(Specifier.substr(1));
+      if (Size < 0) {
+        return std::string("invalid ") + field + "-size field, "
+               "must be positive";
+      }
+
       Split = Token.split(':');
-      unsigned ABIAlign = getInt(Split.first) / 8;
+      int ABIAlignBits = getInt(Split.first);
+      if (ABIAlignBits < 0 || ABIAlignBits % 8 != 0) {
+        return std::string("invalid ") + field +"-abi-alignment field, "
+               "must be a positive 8-bit multiple";
+      }
+      unsigned ABIAlign = ABIAlignBits / 8;
 
       Split = Split.second.split(':');
-      unsigned PrefAlign = getInt(Split.first) / 8;
+
+      int PrefAlignBits = getInt(Split.first);
+      if (PrefAlignBits < 0 || PrefAlignBits % 8 != 0) {
+        return std::string("invalid ") + field +"-preferred-alignment field, "
+               "must be a positive 8-bit multiple";
+      }
+      unsigned PrefAlign = PrefAlignBits / 8;
       if (PrefAlign == 0)
         PrefAlign = ABIAlign;
-      setAlignment(AlignType, ABIAlign, PrefAlign, Size);
+      
+      if (td)
+        td->setAlignment(AlignType, ABIAlign, PrefAlign, Size);
       break;
     }
     case 'n':  // Native integer types.
       Specifier = Specifier.substr(1);
       do {
-        if (unsigned Width = getInt(Specifier))
-          LegalIntWidths.push_back(Width);
+        int Width = getInt(Specifier);
+        if (Width <= 0) {
+          return std::string("invalid native integer size \'") + Specifier.str() +
+                 "\', must be a positive integer.";
+        }
+        if (td && Width != 0)
+          td->LegalIntWidths.push_back(Width);
         Split = Token.split(':');
         Specifier = Split.first;
         Token = Split.second;
       } while (!Specifier.empty() || !Token.empty());
       break;
-    case 'S': // Stack natural alignment.
-      StackNaturalAlign = getInt(Specifier.substr(1));
-      StackNaturalAlign /= 8;
-      // FIXME: Should we really be truncating these alingments and
-      // sizes silently?
+    case 'S': { // Stack natural alignment.
+      int StackNaturalAlignBits = getInt(Specifier.substr(1));
+      if (StackNaturalAlignBits < 0 || StackNaturalAlignBits % 8 != 0) {
+        return "invalid natural stack alignment (S-field), "
+               "must be a positive 8-bit multiple";
+      }
+      if (td)
+        td->StackNaturalAlign = StackNaturalAlignBits / 8;
       break;
+    }
     default:
       break;
     }
   }
+
+  return "";
 }
 
 /// Default ctor.
@@ -242,7 +303,9 @@
 
 TargetData::TargetData(const Module *M)
   : ImmutablePass(ID) {
-  init(M->getDataLayout());
+  std::string errMsg = parseSpecifier(M->getDataLayout(), this);
+  assert(errMsg == "" && "Module M has malformed target data layout string.");
+  (void)errMsg;
 }
 
 void