diff --git a/compiler-rt.spec b/compiler-rt.spec
index 68e7d80..e382aca 100644
--- a/compiler-rt.spec
+++ b/compiler-rt.spec
@@ -21,6 +21,7 @@ Source1:	https://github.com/llvm/llvm-project/releases/download/llvmorg-%{versio
 Source2:	tstellar-gpg-key.asc
 
 Patch0:		0001-PATCH-std-thread-copy.patch
+Patch1:		msflags.patch
 
 BuildRequires:	gcc
 BuildRequires:	gcc-c++
diff --git a/msflags.patch b/msflags.patch
new file mode 100644
index 0000000..98b8afb
--- /dev/null
+++ b/msflags.patch
@@ -0,0 +1,47 @@
+diff -Naur compiler-rt-11.1.0rc2.src.orig/cmake/config-ix.cmake compiler-rt-11.1.0rc2.src/cmake/config-ix.cmake
+--- compiler-rt-11.1.0rc2.src.orig/cmake/config-ix.cmake	2021-02-15 15:16:53.000000000 +0100
++++ compiler-rt-11.1.0rc2.src/cmake/config-ix.cmake	2021-02-15 15:27:03.000000000 +0100
+@@ -85,15 +85,15 @@
+   check_cxx_compiler_flag("-fvisibility-inlines-hidden" COMPILER_RT_HAS_FVISIBILITY_INLINES_HIDDEN_FLAG)
+ endif()
+ 
+-check_cxx_compiler_flag(/GR COMPILER_RT_HAS_GR_FLAG)
+-check_cxx_compiler_flag(/GS COMPILER_RT_HAS_GS_FLAG)
+-check_cxx_compiler_flag(/MT COMPILER_RT_HAS_MT_FLAG)
+-check_cxx_compiler_flag(/Oy COMPILER_RT_HAS_Oy_FLAG)
++#check_cxx_compiler_flag(/GR COMPILER_RT_HAS_GR_FLAG)
++#check_cxx_compiler_flag(/GS COMPILER_RT_HAS_GS_FLAG)
++#check_cxx_compiler_flag(/MT COMPILER_RT_HAS_MT_FLAG)
++#check_cxx_compiler_flag(/Oy COMPILER_RT_HAS_Oy_FLAG)
+ 
+ # Debug info flags.
+ check_cxx_compiler_flag(-gline-tables-only COMPILER_RT_HAS_GLINE_TABLES_ONLY_FLAG)
+ check_cxx_compiler_flag(-g COMPILER_RT_HAS_G_FLAG)
+-check_cxx_compiler_flag(/Zi COMPILER_RT_HAS_Zi_FLAG)
++#check_cxx_compiler_flag(/Zi COMPILER_RT_HAS_Zi_FLAG)
+ 
+ # Warnings.
+ check_cxx_compiler_flag(-Wall COMPILER_RT_HAS_WALL_FLAG)
+@@ -108,14 +108,14 @@
+ check_cxx_compiler_flag("-Werror -Wcovered-switch-default" COMPILER_RT_HAS_WCOVERED_SWITCH_DEFAULT_FLAG)
+ check_cxx_compiler_flag(-Wno-pedantic COMPILER_RT_HAS_WNO_PEDANTIC)
+ 
+-check_cxx_compiler_flag(/W4 COMPILER_RT_HAS_W4_FLAG)
+-check_cxx_compiler_flag(/WX COMPILER_RT_HAS_WX_FLAG)
+-check_cxx_compiler_flag(/wd4146 COMPILER_RT_HAS_WD4146_FLAG)
+-check_cxx_compiler_flag(/wd4291 COMPILER_RT_HAS_WD4291_FLAG)
+-check_cxx_compiler_flag(/wd4221 COMPILER_RT_HAS_WD4221_FLAG)
+-check_cxx_compiler_flag(/wd4391 COMPILER_RT_HAS_WD4391_FLAG)
+-check_cxx_compiler_flag(/wd4722 COMPILER_RT_HAS_WD4722_FLAG)
+-check_cxx_compiler_flag(/wd4800 COMPILER_RT_HAS_WD4800_FLAG)
++#check_cxx_compiler_flag(/W4 COMPILER_RT_HAS_W4_FLAG)
++#check_cxx_compiler_flag(/WX COMPILER_RT_HAS_WX_FLAG)
++#check_cxx_compiler_flag(/wd4146 COMPILER_RT_HAS_WD4146_FLAG)
++#check_cxx_compiler_flag(/wd4291 COMPILER_RT_HAS_WD4291_FLAG)
++#check_cxx_compiler_flag(/wd4221 COMPILER_RT_HAS_WD4221_FLAG)
++#check_cxx_compiler_flag(/wd4391 COMPILER_RT_HAS_WD4391_FLAG)
++#check_cxx_compiler_flag(/wd4722 COMPILER_RT_HAS_WD4722_FLAG)
++#check_cxx_compiler_flag(/wd4800 COMPILER_RT_HAS_WD4800_FLAG)
+ 
+ # Symbols.
+ check_symbol_exists(__func__ "" COMPILER_RT_HAS_FUNC_SYMBOL)