diff --git a/lldb/source/Utility/ArchSpec.cpp b/lldb/source/Utility/ArchSpec.cpp
--- a/lldb/source/Utility/ArchSpec.cpp
+++ b/lldb/source/Utility/ArchSpec.cpp
@@ -1443,6 +1443,9 @@
         GetCore() == ArchSpec::Core::eCore_thumbv6m) {
       return true;
     }
+    // Windows on ARM is always thumb.
+    if (GetTriple().isOSWindows())
+      return true;
   }
   return false;
 }
diff --git a/lldb/test/Shell/ObjectFile/PECOFF/disassemble-thumb.yaml b/lldb/test/Shell/ObjectFile/PECOFF/disassemble-thumb.yaml
new file mode 100644
--- /dev/null
+++ b/lldb/test/Shell/ObjectFile/PECOFF/disassemble-thumb.yaml
@@ -0,0 +1,92 @@
+# RUN: yaml2obj %s > %t.exe
+# RUN: %lldb %t.exe -o "disassemble -b -n entry" -b | FileCheck %s
+
+# CHECK: {{.*}}.exe[0x401000] <+0>: 0x0040 lsls   r0, r0, #0x1
+# CHECK: {{.*}}.exe[0x401002] <+2>: 0x4770 bx     lr
+
+--- !COFF
+OptionalHeader:
+  AddressOfEntryPoint: 4097
+  ImageBase:       4194304
+  SectionAlignment: 4096
+  FileAlignment:   512
+  MajorOperatingSystemVersion: 6
+  MinorOperatingSystemVersion: 0
+  MajorImageVersion: 0
+  MinorImageVersion: 0
+  MajorSubsystemVersion: 6
+  MinorSubsystemVersion: 0
+  Subsystem:       IMAGE_SUBSYSTEM_WINDOWS_CUI
+  DLLCharacteristics: [ IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE, IMAGE_DLL_CHARACTERISTICS_NX_COMPAT, IMAGE_DLL_CHARACTERISTICS_TERMINAL_SERVER_AWARE ]
+  SizeOfStackReserve: 1048576
+  SizeOfStackCommit: 4096
+  SizeOfHeapReserve: 1048576
+  SizeOfHeapCommit: 4096
+  ExportTable:
+    RelativeVirtualAddress: 0
+    Size:            0
+  ImportTable:
+    RelativeVirtualAddress: 0
+    Size:            0
+  ResourceTable:
+    RelativeVirtualAddress: 0
+    Size:            0
+  ExceptionTable:
+    RelativeVirtualAddress: 0
+    Size:            0
+  CertificateTable:
+    RelativeVirtualAddress: 0
+    Size:            0
+  BaseRelocationTable:
+    RelativeVirtualAddress: 0
+    Size:            0
+  Debug:
+    RelativeVirtualAddress: 0
+    Size:            0
+  Architecture:
+    RelativeVirtualAddress: 0
+    Size:            0
+  GlobalPtr:
+    RelativeVirtualAddress: 0
+    Size:            0
+  TlsTable:
+    RelativeVirtualAddress: 0
+    Size:            0
+  LoadConfigTable:
+    RelativeVirtualAddress: 0
+    Size:            0
+  BoundImport:
+    RelativeVirtualAddress: 0
+    Size:            0
+  IAT:
+    RelativeVirtualAddress: 0
+    Size:            0
+  DelayImportDescriptor:
+    RelativeVirtualAddress: 0
+    Size:            0
+  ClrRuntimeHeader:
+    RelativeVirtualAddress: 0
+    Size:            0
+header:
+  Machine:         IMAGE_FILE_MACHINE_ARMNT
+  Characteristics: [ IMAGE_FILE_EXECUTABLE_IMAGE, IMAGE_FILE_32BIT_MACHINE ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    VirtualAddress:  4096
+    VirtualSize:     4
+    SectionData:     '40007047'
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+  - Name:            entry
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...