diff --git a/mk/llvm.mk b/mk/llvm.mk
index 9e024ffa9f4..9de04bed598 100644
--- a/mk/llvm.mk
+++ b/mk/llvm.mk
@@ -28,7 +28,7 @@ LLVM_STAMP_$(1) = $$(CFG_LLVM_BUILD_DIR_$(1))/llvm-auto-clean-stamp
 
 $$(LLVM_CONFIG_$(1)): $$(LLVM_DEPS) $$(LLVM_STAMP_$(1))
 	@$$(call E, make: llvm)
-	$$(Q)$$(MAKE) -C $$(CFG_LLVM_BUILD_DIR_$(1)) $$(CFG_LLVM_BUILD_ENV)
+	$$(Q)$$(MAKE) -C $$(CFG_LLVM_BUILD_DIR_$(1)) $$(CFG_LLVM_BUILD_ENV_$(1))
 	$$(Q)touch $$(LLVM_CONFIG_$(1))
 endif
 
diff --git a/mk/platform.mk b/mk/platform.mk
index ac6cf3c5451..c2fe8e98e45 100644
--- a/mk/platform.mk
+++ b/mk/platform.mk
@@ -352,7 +352,7 @@ AR_i686-pc-mingw32=$(AR)
 CFG_LIB_NAME_i686-pc-mingw32=$(1).dll
 CFG_LIB_GLOB_i686-pc-mingw32=$(1)-*.dll
 CFG_LIB_DSYM_GLOB_i686-pc-mingw32=$(1)-*.dylib.dSYM
-CFG_GCCISH_CFLAGS_i686-pc-mingw32 := -Wall -Werror -g -m32 -march=i686 -D_WIN32_WINNT=0x0600
+CFG_GCCISH_CFLAGS_i686-pc-mingw32 := -Wall -Werror -g -m32 -march=i686 -D_WIN32_WINNT=0x0600 -I$(CFG_SRC_DIR)src/etc/mingw-fix-include
 CFG_GCCISH_CXXFLAGS_i686-pc-mingw32 := -fno-rtti
 CFG_GCCISH_LINK_FLAGS_i686-pc-mingw32 := -shared -fPIC -g -m32
 CFG_GCCISH_DEF_FLAG_i686-pc-mingw32 :=
@@ -361,6 +361,7 @@ CFG_GCCISH_POST_LIB_FLAGS_i686-pc-mingw32 :=
 CFG_DEF_SUFFIX_i686-pc-mingw32 := .mingw32.def
 CFG_INSTALL_NAME_i686-pc-mingw32 =
 CFG_LIBUV_LINK_FLAGS_i686-pc-mingw32 := -lWs2_32 -lpsapi -liphlpapi
+CFG_LLVM_BUILD_ENV_i686-pc-mingw32 := CPATH=$(CFG_SRC_DIR)src/etc/mingw-fix-include
 CFG_EXE_SUFFIX_i686-pc-mingw32 := .exe
 CFG_WINDOWSY_i686-pc-mingw32 := 1
 CFG_UNIXY_i686-pc-mingw32 :=
diff --git a/mk/rt.mk b/mk/rt.mk
index 35ee42f9cb4..daaf313e01b 100644
--- a/mk/rt.mk
+++ b/mk/rt.mk
@@ -24,7 +24,7 @@
 # working under these assumptions).
 
 # Hack for passing flags into LIBUV, see below.
-LIBUV_FLAGS_i386 = -m32 -fPIC
+LIBUV_FLAGS_i386 = -m32 -fPIC -I$(S)src/etc/mingw-fix-include
 LIBUV_FLAGS_x86_64 = -m64 -fPIC
 ifeq ($(OSTYPE_$(1)), linux-androideabi)
 LIBUV_FLAGS_arm = -fPIC -DANDROID -std=gnu99
diff --git a/src/etc/mingw-fix-include/README.txt b/src/etc/mingw-fix-include/README.txt
new file mode 100644
index 00000000000..876db17a248
--- /dev/null
+++ b/src/etc/mingw-fix-include/README.txt
@@ -0,0 +1,6 @@
+The purpose of these headers is to fix issues with mingw v4.0, as described in #9246.
+
+This works by adding this directory to GCC include search path before mingw system headers directories, 
+so we can intercept their inclusions and add missing definitions without having to modify files in mingw/include.
+
+Once mingw fixes all 3 issues mentioned in #9246, this directory and all references to it from rust/mk/* may be removed.
diff --git a/src/etc/mingw-fix-include/bits/c++config.h b/src/etc/mingw-fix-include/bits/c++config.h
new file mode 100644
index 00000000000..4520779e275
--- /dev/null
+++ b/src/etc/mingw-fix-include/bits/c++config.h
@@ -0,0 +1,8 @@
+#ifndef _FIX_CXXCONFIG_H
+#define _FIX_CXXCONFIG_H 1
+
+#define _GLIBCXX_HAVE_FENV_H 1
+
+#include_next <bits/c++config.h>
+
+#endif
diff --git a/src/etc/mingw-fix-include/winbase.h b/src/etc/mingw-fix-include/winbase.h
new file mode 100644
index 00000000000..3be26d1cb34
--- /dev/null
+++ b/src/etc/mingw-fix-include/winbase.h
@@ -0,0 +1,8 @@
+#ifndef _FIX_WINBASE_H
+#define _FIX_WINBASE_H 1
+
+#define NTDDK_VERSION NTDDI_VERSION
+
+#include_next <winbase.h>
+
+#endif
diff --git a/src/etc/mingw-fix-include/winsock2.h b/src/etc/mingw-fix-include/winsock2.h
new file mode 100644
index 00000000000..36b58dcd1ee
--- /dev/null
+++ b/src/etc/mingw-fix-include/winsock2.h
@@ -0,0 +1,12 @@
+#ifndef _FIX_WINSOCK2_H
+#define _FIX_WINSOCK2_H 1
+
+#include_next <winsock2.h>
+
+typedef struct pollfd {
+  SOCKET fd;
+  short  events;
+  short  revents;
+} WSAPOLLFD, *PWSAPOLLFD, *LPWSAPOLLFD;
+
+#endif