diff --git a/MozillaFirefox.changes b/MozillaFirefox.changes
index f0898c78..ade4856f 100644
--- a/MozillaFirefox.changes
+++ b/MozillaFirefox.changes
@@ -32,6 +32,10 @@ Sat May 29 20:55:56 UTC 2021 - Wolfgang Rosenauer <wr@rosenauer.org>
   rust-cbindgen >= 0.19.0
 - do not rely on nodejs10 packagename anymore
 - updated mozilla.keyring
+- switched TW/x86_64 to clang as the last platform due to
+  https://bugs.gentoo.org/792705
+- but LTO with clang is broken in TW so disable LTO for it
+  https://bugs.llvm.org/show_bug.cgi?id=47872
 
 -------------------------------------------------------------------
 Thu May  6 13:40:10 UTC 2021 - Guillaume GARDET <guillaume.gardet@opensuse.org>
diff --git a/MozillaFirefox.spec b/MozillaFirefox.spec
index 2c191127..c1953653 100644
--- a/MozillaFirefox.spec
+++ b/MozillaFirefox.spec
@@ -45,13 +45,6 @@
 
 # upstream default is clang (to use gcc for large parts set to 0)
 %define clang_build    1
-%if 0%{?is_opensuse} && 0%{?suse_version} >= 1550
-%ifarch x86_64
-# on Tumbleweed/x86_64 this does not work due to undefined
-#  references to `__rust_probestack'
-%define clang_build    1
-%endif
-%endif
 
 # PIE, full relro
 %define build_hardened 1
@@ -512,10 +505,10 @@ ac_add_options --enable-optimize="-O1"
 %endif
 %ifarch x86_64
 # LTO needs newer toolchain stack only (at least GCC 8.2.1 (r268506)
-%if 0%{?suse_version} > 1500
-#ac_add_options --enable-lto
+%if 0%{?suse_version} > 1500 && 0%{?suse_version} < 1550
+ac_add_options --enable-lto
 %if 0%{?do_profiling}
-#ac_add_options MOZ_PGO=1
+ac_add_options MOZ_PGO=1
 %endif
 %endif
 %endif