diff --git a/configure b/configure
index 5733793382..f20a6883a0 100755
--- a/configure
+++ b/configure
@@ -4817,6 +4817,47 @@ fi
   if test -n "$NOT_THE_CFLAGS"; then
     CFLAGS="$CFLAGS -Wno-compound-token-split-by-macro"
   fi
+  # Similarly remove clang 15+'s deprecated-non-prototype, as it warns about
+  # tree-walking APIs that we can't reasonably change in the back branches.
+  NOT_THE_CFLAGS=""
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC supports -Wdeprecated-non-prototype" >&5
+$as_echo_n "checking whether $CC supports -Wdeprecated-non-prototype... " >&6; }
+if ${pgac_cv_prog_cc_cflags__Wdeprecated_non_prototype+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+CFLAGS="$pgac_save_CFLAGS -Wdeprecated-non-prototype"
+ac_save_c_werror_flag=$ac_c_werror_flag
+ac_c_werror_flag=yes
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  pgac_cv_prog_cc_cflags__Wdeprecated_non_prototype=yes
+else
+  pgac_cv_prog_cc_cflags__Wdeprecated_non_prototype=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+ac_c_werror_flag=$ac_save_c_werror_flag
+CFLAGS="$pgac_save_CFLAGS"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_prog_cc_cflags__Wdeprecated_non_prototype" >&5
+$as_echo "$pgac_cv_prog_cc_cflags__Wdeprecated_non_prototype" >&6; }
+if test x"$pgac_cv_prog_cc_cflags__Wdeprecated_non_prototype" = x"yes"; then
+  NOT_THE_CFLAGS="${NOT_THE_CFLAGS} -Wdeprecated-non-prototype"
+fi
+
+  if test -n "$NOT_THE_CFLAGS"; then
+    CFLAGS="$CFLAGS -Wno-deprecated-non-prototype"
+  fi
   # Similarly disable useless truncation warnings from gcc 8+
   NOT_THE_CFLAGS=""
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CC supports -Wformat-truncation" >&5
diff --git a/configure.in b/configure.in
index a30904abc6..ee85d686e2 100644
--- a/configure.in
+++ b/configure.in
@@ -461,6 +461,13 @@ if test "$GCC" = yes -a "$ICC" = no; then
   if test -n "$NOT_THE_CFLAGS"; then
     CFLAGS="$CFLAGS -Wno-compound-token-split-by-macro"
   fi
+  # Similarly remove clang 15+'s deprecated-non-prototype, as it warns about
+  # tree-walking APIs that we can't reasonably change in the back branches.
+  NOT_THE_CFLAGS=""
+  PGAC_PROG_CC_VAR_OPT(NOT_THE_CFLAGS, [-Wdeprecated-non-prototype])
+  if test -n "$NOT_THE_CFLAGS"; then
+    CFLAGS="$CFLAGS -Wno-deprecated-non-prototype"
+  fi
   # Similarly disable useless truncation warnings from gcc 8+
   NOT_THE_CFLAGS=""
   PGAC_PROG_CC_VAR_OPT(NOT_THE_CFLAGS, [-Wformat-truncation])