Index: lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
===================================================================
--- lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
+++ lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
@@ -90,6 +90,7 @@
 
   PrivateGlobalPrefix = "$M";
   PrivateLabelPrefix = "$M";
+  CommentString = ";";
 }
 
 void ARMCOFFMCAsmInfoGNU::anchor() { }
Index: test/MC/ARM/Windows/literals-comments.s
===================================================================
--- /dev/null
+++ test/MC/ARM/Windows/literals-comments.s
@@ -0,0 +1,13 @@
+; RUN: llvm-mc -triple armv7-windows-msvc -filetype obj -o - %s
+
+	.syntax unified
+	.thumb
+
+	.text
+
+	.global function
+	.thumb_func
+function:
+	; this is a comment
+	mov r0, #42 ; this # was not
+	bx lr