diff --git a/overlay/MANIFEST b/overlay/MANIFEST
index 7dd79e5..c72fff7 100644
--- a/overlay/MANIFEST
+++ b/overlay/MANIFEST
@@ -225,6 +225,7 @@ new	-	bazel/public-patches/curl_private_lib_includes.patch
 new	-	bazel/public-patches/google_benchmark_gnu_driver_flags.patch
 new	-	bazel/public-patches/llvm_windows_absolute_symlinks.patch
 new	-	bazel/public-patches/llvm_windows_stack_flag.patch
+new	-	bazel/public-patches/llvm_windows_target_triple.patch
 new	-	bazel/public-patches/mimalloc.BUILD
 new	-	bazel/public-patches/protobuf_windows_link_libs.patch
 new	-	bazel/public-patches/rules_cc_copy_dynamic_libraries_same_package.patch
diff --git a/overlay/MODULE.bazel b/overlay/MODULE.bazel
index e667ea1..bbaeed5 100644
--- a/overlay/MODULE.bazel
+++ b/overlay/MODULE.bazel
@@ -57,6 +57,7 @@ llvm_source = use_extension("//bazel/public-patches:llvm_source.bzl", "llvm_sour
 llvm_source.configure(extra_patches = [
     "//bazel/public-patches:llvm_windows_stack_flag.patch",
     "//bazel/public-patches:llvm_windows_absolute_symlinks.patch",
+    "//bazel/public-patches:llvm_windows_target_triple.patch",
 ])
 
 use_repo(llvm_source, "llvm-raw")
diff --git a/overlay/bazel/public-patches/llvm_windows_target_triple.patch b/overlay/bazel/public-patches/llvm_windows_target_triple.patch
new file mode 100644
index 0000000..d14acfe
--- /dev/null
+++ b/overlay/bazel/public-patches/llvm_windows_target_triple.patch
@@ -0,0 +1,26 @@
+--- a/utils/bazel/llvm-project-overlay/llvm/config.bzl
++++ b/utils/bazel/llvm-project-overlay/llvm/config.bzl
+@@ -144,7 +144,22 @@
+     Label("//llvm:is_aarch64_windows_clang_mingw"): native_arch_defines("AArch64", "aarch64-w64-windows-gnu"),
+     Label("//llvm:is_aarch64_windows_clang_cl"): native_arch_defines("AArch64", "aarch64-pc-windows-msvc"),
+     Label("//llvm:is_aarch64_windows_msvc"): native_arch_defines("AArch64", "aarch64-pc-windows-msvc"),
+-    Label("//llvm:is_x86_64_windows_clang_mingw"): native_arch_defines("X86", "x86_64-w64-windows-gnu"),
++    # The name of this arm says mingw, but the condition underneath it is just
++    # "Windows, and the compiler is clang", which is us. We are clang driving
++    # lld-link with --target=x86_64-pc-windows-msvc against a Microsoft sysroot,
++    # and the pair of triples this bakes in is the only thing in the whole build
++    # that says GNU.
++    #
++    # They are what the compiler falls back on when nothing on the command line
++    # names a target, which is the case for mojo run. The code it generates then
++    # asks for ___chkstk_ms and __main, which are libgcc and mingw entry points,
++    # and the JIT cannot resolve them because a Windows machine has no reason to
++    # have either one.
++    #
++    # Only the x86_64 arm is touched. The aarch64 one above has the same problem,
++    # but nothing here builds for that target, so there is no way to find out
++    # whether it is the only thing wrong with it.
++    Label("//llvm:is_x86_64_windows_clang_mingw"): native_arch_defines("X86", "x86_64-pc-windows-msvc"),
+     Label("//llvm:darwin_arm64"): native_arch_defines("AArch64", "arm64-apple-darwin"),
+     Label("//llvm:darwin_x86_64"): native_arch_defines("X86", "x86_64-unknown-darwin"),
+     Label("//llvm:linux_aarch64"): native_arch_defines("AArch64", "aarch64-unknown-linux-gnu"),