diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
@@ -91,7 +91,7 @@
   ExceptionsType = ExceptionHandling::WinEH;
   PrivateGlobalPrefix = "$M";
   PrivateLabelPrefix = "$M";
-  CommentString = ";";
+  CommentString = "@";
 
   // Conditional Thumb 4-byte instructions can have an implicit IT.
   MaxInstLength = 6;
diff --git a/llvm/test/CodeGen/ARM/cfguard-checks.ll b/llvm/test/CodeGen/ARM/cfguard-checks.ll
--- a/llvm/test/CodeGen/ARM/cfguard-checks.ll
+++ b/llvm/test/CodeGen/ARM/cfguard-checks.ll
@@ -101,8 +101,8 @@
 	; CHECK:       blx r1
   ; CHECK-NEXT:  $Mtmp0:
 	; CHECK-NEXT:  blx r4
-  ; CHECK:       ; %common.ret
-  ; CHECK:       ; %lpad
+  ; CHECK:       @ %common.ret
+  ; CHECK:       @ %lpad
 }
 
 declare void @h()
diff --git a/llvm/test/MC/ARM/Windows/literals-comments.s b/llvm/test/MC/ARM/Windows/literals-comments.s
--- a/llvm/test/MC/ARM/Windows/literals-comments.s
+++ b/llvm/test/MC/ARM/Windows/literals-comments.s
@@ -1,4 +1,4 @@
-; RUN: llvm-mc -triple armv7-windows-msvc -filetype obj -o - %s
+@ RUN: llvm-mc -triple armv7-windows-msvc -filetype obj -o - %s
 
   .syntax unified
   .thumb
@@ -8,6 +8,6 @@
   .global function
   .thumb_func
 function:
-  ; this is a comment
-  mov r0, #42 ; this # was not
+  @ this is a comment
+  mov r0, #42 @ this # was not
   bx lr