diff --git a/clang/lib/Driver/ToolChains/MinGW.cpp b/clang/lib/Driver/ToolChains/MinGW.cpp
--- a/clang/lib/Driver/ToolChains/MinGW.cpp
+++ b/clang/lib/Driver/ToolChains/MinGW.cpp
@@ -348,6 +348,15 @@
                                          Exec, CmdArgs, Inputs, Output));
 }
 
+static bool isCrossCompiling(const llvm::Triple &T, bool RequireArchMatch) {
+  llvm::Triple HostTriple(llvm::Triple::normalize(LLVM_HOST_TRIPLE));
+  if (HostTriple.getOS() != llvm::Triple::Win32)
+    return true;
+  if (RequireArchMatch && HostTriple.getArch() != T.getArch())
+    return true;
+  return false;
+}
+
 // Simplified from Generic_GCC::GCCInstallationDetector::ScanLibDirForGCCTriple.
 static bool findGccVersion(StringRef LibDir, std::string &GccLibDir,
                            std::string &Ver,
@@ -487,7 +496,13 @@
   getFilePaths().push_back(
       (Base + SubdirName + llvm::sys::path::get_separator() + "mingw/lib").str());
 
-  getFilePaths().push_back(Base + "lib");
+  // Only include <base>/lib if we're not cross compiling (not even for
+  // windows->windows to a different arch), or if the sysroot has been set
+  // (where we presume the user has pointed it at an arch specific
+  // subdirectory).
+  if (!::isCrossCompiling(getTriple(), /*RequireArchMatch=*/true) ||
+      getDriver().SysRoot.size())
+    getFilePaths().push_back(Base + "lib");
 
   NativeLLVMSupport =
       Args.getLastArgValue(options::OPT_fuse_ld_EQ, CLANG_DEFAULT_LINKER)
@@ -649,7 +664,13 @@
   addSystemInclude(DriverArgs, CC1Args,
                    Base + SubdirName + llvm::sys::path::get_separator() + "usr/include");
 
-  addSystemInclude(DriverArgs, CC1Args, Base + "include");
+  // Only include <base>/include if we're not cross compiling (but do allow it
+  // if we're on Windows and building for Windows on another architecture),
+  // or if the sysroot has been set (where we presume the user has pointed it
+  // at an arch specific subdirectory).
+  if (!::isCrossCompiling(getTriple(), /*RequireArchMatch=*/false) ||
+      getDriver().SysRoot.size())
+    addSystemInclude(DriverArgs, CC1Args, Base + "include");
 }
 
 void toolchains::MinGW::addClangTargetOptions(
diff --git a/clang/test/Driver/mingw-sysroot.cpp b/clang/test/Driver/mingw-sysroot.cpp
--- a/clang/test/Driver/mingw-sysroot.cpp
+++ b/clang/test/Driver/mingw-sysroot.cpp
@@ -22,7 +22,12 @@
 // If we find a gcc in the path with the right triplet prefix, pick that as
 // sysroot:
 
-// RUN: env "PATH=%T/testroot-gcc/bin:%PATH%" %clang -target x86_64-w64-mingw32 -rtlib=platform -stdlib=libstdc++ --sysroot="" -c -### %s 2>&1 | FileCheck -check-prefix=CHECK_TESTROOT_GCC %s
+// This test is only executed on non-Windows systems, i.e. only when
+// cross compiling. Check that we don't add the tool root's plain include
+// directory to the path - this would end up including /usr/include for
+// cross toolchains installed in /usr.
+
+// RUN: env "PATH=%T/testroot-gcc/bin:%PATH%" %clang -target x86_64-w64-mingw32 -rtlib=platform -stdlib=libstdc++ --sysroot="" -c -### %s 2>&1 | FileCheck -check-prefix=CHECK_TESTROOT_GCC %s --implicit-check-not="\"{{.*}}/testroot-gcc{{/|\\\\}}include\""
 // CHECK_TESTROOT_GCC: "-internal-isystem" "[[BASE:[^"]+]]/testroot-gcc{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}10.2-posix{{/|\\\\}}include{{/|\\\\}}c++"
 // CHECK_TESTROOT_GCC-SAME: {{^}} "-internal-isystem" "[[BASE]]/testroot-gcc{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}10.2-posix{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}x86_64-w64-mingw32"
 // CHECK_TESTROOT_GCC-SAME: {{^}} "-internal-isystem" "[[BASE]]/testroot-gcc{{/|\\\\}}lib{{/|\\\\}}gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}10.2-posix{{/|\\\\}}include{{/|\\\\}}c++{{/|\\\\}}backward"
@@ -32,6 +37,13 @@
 // CHECK_TESTROOT_GCC: "-internal-isystem" "[[BASE]]/testroot-gcc{{/|\\\\}}x86_64-w64-mingw32{{/|\\\\}}include"
 
 
+// If we pass --sysroot explicitly, then we do include <sysroot>/include
+// even when cross compiling.
+// RUN: %clang -target x86_64-w64-mingw32 -rtlib=platform -stdlib=libstdc++ --sysroot="%T/testroot-gcc" -c -### %s 2>&1 | FileCheck -check-prefix=CHECK_TESTROOT_GCC_EXPLICIT %s
+
+// CHECK_TESTROOT_GCC_EXPLICIT: "-internal-isystem" "{{[^"]+}}/testroot-gcc{{/|\\\\}}include"
+
+
 // If there's a matching sysroot next to the clang binary itself, prefer that
 // over a gcc in the path: