diff --git a/thunderbird.spec b/thunderbird.spec
index 5affaf1..032387d 100644
--- a/thunderbird.spec
+++ b/thunderbird.spec
@@ -1019,8 +1019,12 @@ echo "ac_add_options --with-mozilla-api-keyfile=`pwd`/mozilla-api-key" >> .mozco
 echo "ac_add_options --with-google-location-service-api-keyfile=`pwd`/google-loc-api-key" >> .mozconfig
 echo "ac_add_options --with-google-safebrowsing-api-keyfile=`pwd`/google-api-key" >> .mozconfig
 
+# May result in empty --with-libclang-path= in earlier versions.
+# So far this is needed only for c8s.
+%if 0%{?rhel} == 8 && %{rhel_minor_version} >= 10
 # Clang 17 upstream's detection fails, tell it where to look.
 echo "ac_add_options --with-libclang-path=`llvm-config --libdir`" >> .mozconfig
+%endif
 
 echo 'export NODEJS="%{_buildrootdir}/bin/node-stdout-nonblocking-wrapper"' >> .mozconfig