diff --git a/llvm/lib/Target/SystemZ/AsmParser/SystemZAsmParser.cpp b/llvm/lib/Target/SystemZ/AsmParser/SystemZAsmParser.cpp
--- a/llvm/lib/Target/SystemZ/AsmParser/SystemZAsmParser.cpp
+++ b/llvm/lib/Target/SystemZ/AsmParser/SystemZAsmParser.cpp
@@ -830,7 +830,7 @@
   }
 
   // Handle register names of the form %<prefix><number>
-  if (Parser.getTok().is(AsmToken::Percent)) {
+  if (isParsingATT() && Parser.getTok().is(AsmToken::Percent)) {
     if (parseRegister(Reg))
       return MatchOperand_ParseFail;
 
@@ -912,6 +912,9 @@
     Operands.push_back(SystemZOperand::createImm(Register, StartLoc, EndLoc));
   }
   else {
+    if (isParsingHLASM())
+      return MatchOperand_NoMatch;
+
     Register Reg;
     if (parseRegister(Reg))
       return MatchOperand_ParseFail;
@@ -1019,7 +1022,7 @@
   if (getLexer().is(AsmToken::LParen)) {
     Parser.Lex();
 
-    if (getLexer().is(AsmToken::Percent)) {
+    if (isParsingATT() && getLexer().is(AsmToken::Percent)) {
       // Parse the first register.
       HaveReg1 = true;
       if (parseRegister(Reg1))
@@ -1062,7 +1065,7 @@
         if (parseIntegerRegister(Reg2, RegGR))
           return true;
       } else {
-        if (parseRegister(Reg2))
+        if (isParsingATT() && parseRegister(Reg2))
           return true;
       }
     }
@@ -1419,7 +1422,7 @@
   // a context-dependent parse routine, which gives the required register
   // class.  The code is here to mop up other cases, like those where
   // the instruction isn't recognized.
-  if (Parser.getTok().is(AsmToken::Percent)) {
+  if (isParsingATT() && Parser.getTok().is(AsmToken::Percent)) {
     Register Reg;
     if (parseRegister(Reg))
       return true;