diff --git a/ares/m4/cares-compilers.m4 b/ares/m4/cares-compilers.m4
index 0dc2b0312..4ffa0d25d 100644
--- a/ares/m4/cares-compilers.m4
+++ b/ares/m4/cares-compilers.m4
@@ -331,8 +331,12 @@ AC_DEFUN([CARES_SET_COMPILER_BASIC_OPTS], [
         #
       HPUXC)
         #
-        dnl Placeholder
-        tmp_CFLAGS="$tmp_CFLAGS"
+        dnl Disallow run-time dereferencing of null pointers
+        tmp_CFLAGS="$tmp_CFLAGS -z"
+        dnl Disable some remarks
+        dnl #4227: padding struct with n bytes to align member
+        dnl #4255: padding size of struct with n bytes to alignment boundary
+        tmp_CFLAGS="$tmp_CFLAGS +W 4227,4255"
         ;;
         #
       IBMC)
diff --git a/m4/curl-compilers.m4 b/m4/curl-compilers.m4
index 20791da98..729d41364 100644
--- a/m4/curl-compilers.m4
+++ b/m4/curl-compilers.m4
@@ -337,8 +337,12 @@ AC_DEFUN([CURL_SET_COMPILER_BASIC_OPTS], [
         #
       HPUXC)
         #
-        dnl Placeholder
-        tmp_CFLAGS="$tmp_CFLAGS"
+        dnl Disallow run-time dereferencing of null pointers
+        tmp_CFLAGS="$tmp_CFLAGS -z"
+        dnl Disable some remarks
+        dnl #4227: padding struct with n bytes to align member
+        dnl #4255: padding size of struct with n bytes to alignment boundary
+        tmp_CFLAGS="$tmp_CFLAGS +W 4227,4255"
         ;;
         #
       IBMC)