diff --git a/debian/changelog b/debian/changelog
index 72296094..619fa137 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -9,6 +9,12 @@ llvm-toolchain-11 (1:11.0.0~+rc2-2) unstable; urgency=medium
   * Also link against -latomic on mipsel to fix
    /usr/[...]/atomic_base.h:426: undefined reference to `__atomic_load_8'
    for lld to fix the FTBFS
+  * Fix a FTBFS on armel with libcxx-armhf-ftbfs.diff
+    atomic:2780:16: error: use of undeclared identifier '__libcpp_signed_lock_free'
+    typedef atomic<__libcpp_signed_lock_free> atomic_signed_lock_free;
+               ^
+    atomic:2781:16: error: unknown type name '__libcpp_unsigned_lock_free'; did you mean 'atomic_signed_lock_free'?
+    typedef atomic<__libcpp_unsigned_lock_free> atomic_unsigned_lock_free;
 
  -- Sylvestre Ledru <sylvestre@debian.org>  Tue, 25 Aug 2020 10:44:00 +0200
 
diff --git a/debian/patches/libcxx-armhf-ftbfs.diff b/debian/patches/libcxx-armhf-ftbfs.diff
new file mode 100644
index 00000000..8d45e281
--- /dev/null
+++ b/debian/patches/libcxx-armhf-ftbfs.diff
@@ -0,0 +1,20 @@
+Index: llvm-toolchain-11-11.0.0~+rc2/libcxx/include/atomic
+===================================================================
+--- llvm-toolchain-11-11.0.0~+rc2.orig/libcxx/include/atomic
++++ llvm-toolchain-11-11.0.0~+rc2/libcxx/include/atomic
+@@ -2775,10 +2775,15 @@ typedef conditional<_LIBCPP_CONTENTION_L
+ typedef conditional<_LIBCPP_CONTENTION_LOCK_FREE, __cxx_contention_t, unsigned char>::type      __libcpp_unsigned_lock_free;
+ #else
+     // No signed/unsigned lock-free types
++#define NO_LOCK_FREE
+ #endif
+ 
++#ifndef NO_LOCK_FREE
+ typedef atomic<__libcpp_signed_lock_free> atomic_signed_lock_free;
+ typedef atomic<__libcpp_unsigned_lock_free> atomic_unsigned_lock_free;
++#endif
++
++#undef NO_LOCK_FREE
+ 
+ #define ATOMIC_FLAG_INIT {false}
+ #define ATOMIC_VAR_INIT(__v) {__v}
diff --git a/debian/patches/series b/debian/patches/series
index c17f4ad1..2b9bdb58 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -136,3 +136,4 @@ disable-fuzzer-compiler-rt-x86.diff
 
 python3-shebang.patch
 print-lldb-path.patch
+libcxx-armhf-ftbfs.diff