Index: lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
===================================================================
--- lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
+++ lib/Target/ARM/MCTargetDesc/ARMMCTargetDesc.cpp
@@ -166,7 +166,10 @@
       ArchFS = FS;
   }
 
-  return createARMMCSubtargetInfoImpl(TT, CPU, ArchFS);
+  MCSubtargetInfo *Info = createARMMCSubtargetInfoImpl(TT, CPU, ArchFS);
+  if (TT.isOSWindows() && !Info->hasFeature(ARM::FeatureNoARM))
+    Info->ToggleFeature(ARM::FeatureNoARM);
+  return Info;
 }
 
 static MCInstrInfo *createARMMCInstrInfo() {
Index: test/MC/ARM/arm-thumb-cpus.s
===================================================================
--- test/MC/ARM/arm-thumb-cpus.s
+++ test/MC/ARM/arm-thumb-cpus.s
@@ -19,6 +19,9 @@
 @ RUN: not llvm-mc -show-encoding -triple=armv6sm-eabi < %s 2>&1 \
 @ RUN:  | FileCheck %s --check-prefix=CHECK-THUMB-ONLY
 
+@ RUN: not llvm-mc -show-encoding -triple=thumbv7-win32-gnu < %s 2>&1 \
+@ RUN:  | FileCheck %s --check-prefix=CHECK-THUMB-ONLY
+
         @ Make sure correct diagnostics are given for CPUs without support for
         @ one or other of the execution states.
         .thumb