diff --git a/tools/llvm-mc/AsmLexer.h b/tools/llvm-mc/AsmLexer.h
index ce292f66b12..c0b32232abb 100644
--- a/tools/llvm-mc/AsmLexer.h
+++ b/tools/llvm-mc/AsmLexer.h
@@ -62,7 +62,9 @@ public:
   bool EnterIncludeFile(const std::string &Filename);
   
   void PrintMessage(SMLoc Loc, const std::string &Msg, const char *Type) const;
-  
+
+  const MCAsmInfo &getMAI() const { return MAI; }
+
 private:
   int getNextChar();
   AsmToken ReturnError(const char *Loc, const std::string &Msg);
diff --git a/tools/llvm-mc/AsmParser.cpp b/tools/llvm-mc/AsmParser.cpp
index d4af4bd0df6..0e7c3443d5a 100644
--- a/tools/llvm-mc/AsmParser.cpp
+++ b/tools/llvm-mc/AsmParser.cpp
@@ -1278,6 +1278,13 @@ bool AsmParser::ParseDirectiveComm(bool IsLocal) {
     Pow2AlignmentLoc = Lexer.getLoc();
     if (ParseAbsoluteExpression(Pow2Alignment))
       return true;
+    
+    // If this target takes alignments in bytes (not log) validate and convert.
+    if (Lexer.getMAI().getAlignmentIsInBytes()) {
+      if (!isPowerOf2_64(Pow2Alignment))
+        return Error(Pow2AlignmentLoc, "alignment must be a power of 2");
+      Pow2Alignment = Log2_64(Pow2Alignment);
+    }
   }
   
   if (Lexer.isNot(AsmToken::EndOfStatement))