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
@@ -979,7 +979,16 @@
 
   const llvm::Triple::VendorType lhs_triple_vendor = lhs_triple.getVendor();
   const llvm::Triple::VendorType rhs_triple_vendor = rhs_triple.getVendor();
-  if (lhs_triple_vendor != rhs_triple_vendor) {
+
+  const llvm::Triple::OSType lhs_triple_os = lhs_triple.getOS();
+  const llvm::Triple::OSType rhs_triple_os = rhs_triple.getOS();
+
+  bool both_windows = lhs_triple.isOSWindows() && rhs_triple.isOSWindows();
+
+  // On Windows, the vendor field doesn't have any practical effect, but
+  // it is often set to either "pc" or "w64".
+  if ((lhs_triple_vendor != rhs_triple_vendor) &&
+      (exact_match || !both_windows)) {
     const bool rhs_vendor_specified = rhs.TripleVendorWasSpecified();
     const bool lhs_vendor_specified = TripleVendorWasSpecified();
     // Both architectures had the vendor specified, so if they aren't equal
@@ -993,8 +1002,6 @@
       return false;
   }
 
-  const llvm::Triple::OSType lhs_triple_os = lhs_triple.getOS();
-  const llvm::Triple::OSType rhs_triple_os = rhs_triple.getOS();
   const llvm::Triple::EnvironmentType lhs_triple_env =
       lhs_triple.getEnvironment();
   const llvm::Triple::EnvironmentType rhs_triple_env =
@@ -1032,6 +1039,9 @@
       return true;
   }
 
+  if (!exact_match && both_windows)
+    return true; // The Windows environments (MSVC vs GNU) are compatible
+
   return IsCompatibleEnvironment(lhs_triple_env, rhs_triple_env);
 }
 
diff --git a/lldb/test/Shell/ObjectFile/PECOFF/settings-abi-i686.yaml b/lldb/test/Shell/ObjectFile/PECOFF/settings-abi-i686.yaml
new file mode 100644
--- /dev/null
+++ b/lldb/test/Shell/ObjectFile/PECOFF/settings-abi-i686.yaml
@@ -0,0 +1,61 @@
+## Check that i386 executables can be opened in both ABI modes.
+## I386 executables are special in the sense that the PECOFF object
+## file plugin returns two architectures for them, i386 and i686, which
+## causes more elaborate comparisons to be run against the Platform plugin's
+## architecture list. Check that this is accepted despite potential mismatches
+## in the environment part of the triple.
+
+# RUN: yaml2obj %s -o %t
+
+## Default ABI is msvc:
+# RUN: %lldb -O "settings set plugin.object-file.pe-coff.abi msvc" \
+# RUN:   -f %t -o "image list --triple --basename" -o exit | \
+# RUN:   FileCheck -DABI=msvc -DFILENAME=%basename_t.tmp %s
+
+## Default ABI is gnu:
+# RUN: %lldb -O "settings set plugin.object-file.pe-coff.abi gnu" \
+# RUN:   -f %t -o "image list --triple --basename" -o exit | \
+# RUN:   FileCheck -DABI=gnu -DFILENAME=%basename_t.tmp %s
+
+# CHECK-LABEL: image list --triple --basename
+# CHECK-NEXT: i686-pc-windows-[[ABI]] [[FILENAME]]
+
+--- !COFF
+OptionalHeader:
+  AddressOfEntryPoint: 4480
+  ImageBase:       268435456
+  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
+header:
+  Machine:         IMAGE_FILE_MACHINE_I386
+  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:     64
+    SectionData:     DEADBEEFBAADF00D
+  - Name:            .data
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ ]
+    VirtualAddress:  8192
+    VirtualSize:     64
+    SectionData:     DEADBEEFBAADF00D
+  - Name:            .debug_info
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_DISCARDABLE, IMAGE_SCN_MEM_READ ]
+    VirtualAddress:  16384
+    VirtualSize:     64
+    SectionData:     DEADBEEFBAADF00D
+symbols:         []
+...