diff --git a/test/tools/llvm-ml/include_by_env_var.asm b/test/tools/llvm-ml/include_by_env_var.asm
deleted file mode 100644
index 78b08946518..00000000000
--- a/test/tools/llvm-ml/include_by_env_var.asm
+++ /dev/null
@@ -1,20 +0,0 @@
-; RUN: INCLUDE=%S llvm-ml -filetype=s %s /Fo - | FileCheck %s
-
-include included.inc
-
-.code
-
-t1:
-mov eax, Const
-
-; CHECK-LABEL: t1:
-; CHECK-NEXT: mov eax, 8
-
-t2:
-push_pop ebx
-
-; CHECK-LABEL: t2:
-; CHECK-NEXT: push ebx
-; CHECK-NEXT: pop ebx
-
-end
diff --git a/test/tools/llvm-ml/include_by_env_var_errors.asm b/test/tools/llvm-ml/include_by_env_var_errors.asm
deleted file mode 100644
index 161c43ac9aa..00000000000
--- a/test/tools/llvm-ml/include_by_env_var_errors.asm
+++ /dev/null
@@ -1,16 +0,0 @@
-; RUN: not llvm-ml -filetype=s %s /Fo - 2>&1 | FileCheck %s --implicit-check-not=error:
-; RUN: INCLUDE=%S not llvm-ml -filetype=s %s /X /Fo - 2>&1 | FileCheck %s --implicit-check-not=error:
-
-; CHECK: :[[# @LINE + 1]]:9: error: Could not find include file 'included.inc'
-include included.inc
-
-.code
-
-t1:
-mov eax, Const
-
-t2:
-; CHECK: :[[# @LINE + 1]]:1: error: invalid instruction mnemonic 'push_pop'
-push_pop ebx
-
-end
diff --git a/tools/llvm-ml/Opts.td b/tools/llvm-ml/Opts.td
index 06871b49ad0..b5ba920c876 100644
--- a/tools/llvm-ml/Opts.td
+++ b/tools/llvm-ml/Opts.td
@@ -73,8 +73,6 @@ def assembly_file : MLJoinedOrSeparate<"Ta">,
 def error_on_warning : MLFlag<"WX">, Alias<fatal_warnings>;
 def parse_only : MLFlag<"Zs">, HelpText<"Run a syntax-check only">,
                  Alias<filetype>, AliasArgs<["null"]>;
-def ignore_include_envvar : MLFlag<"X">,
-                            HelpText<"Ignore the INCLUDE environment variable">;
 
 def tiny_model_support : UnsupportedFlag<"AT">, HelpText<"">;
 def alternate_linker : UnsupportedJoined<"Bl">, HelpText<"">;
@@ -107,6 +105,7 @@ def listing_title : UnsupportedSeparate<"St">, HelpText<"">;
 def listing_false_conditionals : UnsupportedFlag<"Sx">, HelpText<"">;
 def extra_warnings : UnsupportedFlag<"w">, HelpText<"">;
 def warning_level : UnsupportedJoined<"W">, HelpText<"">;
+def ignore_include_envvar : UnsupportedFlag<"X">, HelpText<"">;
 def line_number_info : UnsupportedFlag<"Zd">, HelpText<"">;
 def export_all_symbols : UnsupportedFlag<"Zf">, HelpText<"">;
 def codeview_info : UnsupportedFlag<"Zi">, HelpText<"">;
diff --git a/tools/llvm-ml/llvm-ml.cpp b/tools/llvm-ml/llvm-ml.cpp
index 7fefb9dda95..14f75d0d814 100644
--- a/tools/llvm-ml/llvm-ml.cpp
+++ b/tools/llvm-ml/llvm-ml.cpp
@@ -36,7 +36,6 @@
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
-#include "llvm/Support/Process.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/TargetSelect.h"
@@ -264,21 +263,8 @@ int main(int Argc, char **Argv) {
   SrcMgr.AddNewSourceBuffer(std::move(*BufferPtr), SMLoc());
 
   // Record the location of the include directories so that the lexer can find
-  // included files later.
-  std::vector<std::string> IncludeDirs =
-      InputArgs.getAllArgValues(OPT_include_path);
-  if (!InputArgs.hasArg(OPT_ignore_include_envvar)) {
-    if (llvm::Optional<std::string> cl_include_dir =
-            llvm::sys::Process::GetEnv("INCLUDE")) {
-      SmallVector<StringRef, 8> Dirs;
-      StringRef(*cl_include_dir)
-          .split(Dirs, ";", /*MaxSplit=*/-1, /*KeepEmpty=*/false);
-      IncludeDirs.reserve(IncludeDirs.size() + Dirs.size());
-      for (StringRef Dir : Dirs)
-        IncludeDirs.push_back(Dir.str());
-    }
-  }
-  SrcMgr.setIncludeDirs(IncludeDirs);
+  // it later.
+  SrcMgr.setIncludeDirs(InputArgs.getAllArgValues(OPT_include_path));
 
   std::unique_ptr<MCRegisterInfo> MRI(TheTarget->createMCRegInfo(TripleName));
   assert(MRI && "Unable to create target register info!");