--- a/check-all.sh	Wed Jan 21 21:27:20 2026 +0100
+++ b/check-all.sh	Wed Jan 21 22:03:49 2026 +0100
@@ -40,6 +40,16 @@
   perform_check_cxx
 done
 
+for cxx in clang++ g++; do
+  printf "Check header errors/warnings with $cxx..."
+  if $cxx -o /dev/null -I src \
+      -Werror -Wall -Wextra -pedantic tests/cpptest.cpp ; then
+    echo "ok."
+  else
+    echo "fail."
+  fi
+done
+
 printf "Check w/o szmul builtin... "
 ./configure --debug --disable-szmul-builtin > /dev/null
 perform_check