diff --git a/m4/curl-compilers.m4 b/m4/curl-compilers.m4
index e732a8722..107dc6ab9 100644
--- a/m4/curl-compilers.m4
+++ b/m4/curl-compilers.m4
@@ -886,36 +886,36 @@ AC_DEFUN([CURL_SET_COMPILER_WARNING_OPTS], [
         #
         if test "$want_warnings" = "yes"; then
           tmp_CFLAGS="$tmp_CFLAGS -pedantic"
-          tmp_CFLAGS="$tmp_CFLAGS -Wall -Wextra"
-          tmp_CFLAGS="$tmp_CFLAGS -Wpointer-arith -Wwrite-strings"
-          tmp_CFLAGS="$tmp_CFLAGS -Wshadow"
-          tmp_CFLAGS="$tmp_CFLAGS -Winline -Wnested-externs"
-          tmp_CFLAGS="$tmp_CFLAGS -Wmissing-declarations"
-          tmp_CFLAGS="$tmp_CFLAGS -Wmissing-prototypes"
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [all extra])
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [pointer-arith write-strings])
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [shadow])
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [inline nested-externs])
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [missing-declarations])
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [missing-prototypes])
           tmp_CFLAGS="$tmp_CFLAGS -Wno-long-long"
-          tmp_CFLAGS="$tmp_CFLAGS -Wfloat-equal"
-          tmp_CFLAGS="$tmp_CFLAGS -Wno-multichar -Wsign-compare"
-          tmp_CFLAGS="$tmp_CFLAGS -Wundef"
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [float-equal])
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [no-multichar sign-compare])
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [undef])
           tmp_CFLAGS="$tmp_CFLAGS -Wno-format-nonliteral"
-          tmp_CFLAGS="$tmp_CFLAGS -Wendif-labels -Wstrict-prototypes"
-          tmp_CFLAGS="$tmp_CFLAGS -Wdeclaration-after-statement"
-          tmp_CFLAGS="$tmp_CFLAGS -Wcast-align"
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [endif-labels strict-prototypes])
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [declaration-after-statement])
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [cast-align])
           tmp_CFLAGS="$tmp_CFLAGS -Wno-system-headers"
-          tmp_CFLAGS="$tmp_CFLAGS -Wshorten-64-to-32"
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [shorten-64-to-32])
           #
           dnl Only clang 1.1 or later
           if test "$compiler_num" -ge "101"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wunused"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [unused])
           fi
           #
           dnl Only clang 2.8 or later
           if test "$compiler_num" -ge "208"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wvla"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [vla])
           fi
           #
           dnl Only clang 2.9 or later
           if test "$compiler_num" -ge "209"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wshift-sign-overflow"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [shift-sign-overflow])
           fi
           #
           dnl Only clang 3.2 or later
@@ -926,19 +926,19 @@ AC_DEFUN([CURL_SET_COMPILER_WARNING_OPTS], [
               dnl mingw because the libtool wrapper executable causes them
               ;;
             *)
-              tmp_CFLAGS="$tmp_CFLAGS -Wmissing-variable-declarations"
+              CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [missing-variable-declarations])
               ;;
             esac
           fi
           #
           dnl Only clang 3.6 or later
           if test "$compiler_num" -ge "306"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wdouble-promotion"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [double-promotion])
           fi
           #
           dnl Only clang 3.9 or later
           if test "$compiler_num" -ge "309"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wcomma"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [comma])
             # avoid the varargs warning, fixed in 4.0
             # https://bugs.llvm.org/show_bug.cgi?id=29140
             if test "$compiler_num" -lt "400"; then
@@ -968,43 +968,45 @@ AC_DEFUN([CURL_SET_COMPILER_WARNING_OPTS], [
           fi
           #
           dnl Set of options we believe *ALL* gcc versions support:
-          tmp_CFLAGS="$tmp_CFLAGS -Wall -W"
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [all])
+          tmp_CFLAGS="$tmp_CFLAGS -W"
           #
           dnl Only gcc 1.4 or later
           if test "$compiler_num" -ge "104"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wpointer-arith -Wwrite-strings"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [pointer-arith write-strings])
             dnl If not cross-compiling with a gcc older than 3.0
             if test "x$cross_compiling" != "xyes" ||
               test "$compiler_num" -ge "300"; then
-              tmp_CFLAGS="$tmp_CFLAGS -Wunused -Wshadow"
+              CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [unused shadow])
             fi
           fi
           #
           dnl Only gcc 2.7 or later
           if test "$compiler_num" -ge "207"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Winline -Wnested-externs"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [inline nested-externs])
             dnl If not cross-compiling with a gcc older than 3.0
             if test "x$cross_compiling" != "xyes" ||
               test "$compiler_num" -ge "300"; then
-              tmp_CFLAGS="$tmp_CFLAGS -Wmissing-declarations"
-              tmp_CFLAGS="$tmp_CFLAGS -Wmissing-prototypes"
+              CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [missing-declarations])
+              CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [missing-prototypes])
             fi
           fi
           #
           dnl Only gcc 2.95 or later
           if test "$compiler_num" -ge "295"; then
             tmp_CFLAGS="$tmp_CFLAGS -Wno-long-long"
-            tmp_CFLAGS="$tmp_CFLAGS -Wbad-function-cast"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [bad-function-cast])
           fi
           #
           dnl Only gcc 2.96 or later
           if test "$compiler_num" -ge "296"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wfloat-equal"
-            tmp_CFLAGS="$tmp_CFLAGS -Wno-multichar -Wsign-compare"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [float-equal])
+            tmp_CFLAGS="$tmp_CFLAGS -Wno-multichar"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [sign-compare])
             dnl -Wundef used only if gcc is 2.96 or later since we get
             dnl lots of "`_POSIX_C_SOURCE' is not defined" in system
             dnl headers with gcc 2.95.4 on FreeBSD 4.9
-            tmp_CFLAGS="$tmp_CFLAGS -Wundef"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [undef])
           fi
           #
           dnl Only gcc 2.97 or later
@@ -1023,13 +1025,13 @@ AC_DEFUN([CURL_SET_COMPILER_WARNING_OPTS], [
           #
           dnl Only gcc 3.3 or later
           if test "$compiler_num" -ge "303"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wendif-labels -Wstrict-prototypes"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [endif-labels strict-prototypes])
           fi
           #
           dnl Only gcc 3.4 or later
           if test "$compiler_num" -ge "304"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wdeclaration-after-statement"
-            tmp_CFLAGS="$tmp_CFLAGS -Wold-style-definition"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [declaration-after-statement])
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [old-style-definition])
           fi
           #
           dnl Only gcc 4.0 or later
@@ -1039,15 +1041,17 @@ AC_DEFUN([CURL_SET_COMPILER_WARNING_OPTS], [
           #
           dnl Only gcc 4.2 or later
           if test "$compiler_num" -ge "402"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wcast-align"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [cast-align])
           fi
           #
           dnl Only gcc 4.3 or later
           if test "$compiler_num" -ge "403"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wtype-limits -Wold-style-declaration"
-            tmp_CFLAGS="$tmp_CFLAGS -Wmissing-parameter-type -Wempty-body"
-            tmp_CFLAGS="$tmp_CFLAGS -Wclobbered -Wignored-qualifiers"
-            tmp_CFLAGS="$tmp_CFLAGS -Wconversion -Wno-sign-conversion -Wvla"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [type-limits old-style-declaration])
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [missing-parameter-type empty-body])
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [clobbered ignored-qualifiers])
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [conversion])
+            tmp_CFLAGS="$tmp_CFLAGS -Wno-sign-conversion"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [vla])
             dnl required for -Warray-bounds, included in -Wall
             tmp_CFLAGS="$tmp_CFLAGS -ftree-vrp"
           fi
@@ -1062,7 +1066,7 @@ AC_DEFUN([CURL_SET_COMPILER_WARNING_OPTS], [
           #
           dnl Only gcc 4.6 or later
           if test "$compiler_num" -ge "406"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wdouble-promotion"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [double-promotion])
           fi
           #
           dnl only gcc 4.8 or later
@@ -1077,18 +1081,19 @@ AC_DEFUN([CURL_SET_COMPILER_WARNING_OPTS], [
           #
           dnl Only gcc 6 or later
           if test "$compiler_num" -ge "600"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wshift-negative-value"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [shift-negative-value])
             tmp_CFLAGS="$tmp_CFLAGS -Wshift-overflow=2"
-            tmp_CFLAGS="$tmp_CFLAGS -Wnull-dereference -fdelete-null-pointer-checks"
-            tmp_CFLAGS="$tmp_CFLAGS -Wduplicated-cond"
-            tmp_CFLAGS="$tmp_CFLAGS -Wunused-const-variable"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [null-dereference])
+            tmp_CFLAGS="$tmp_CFLAGS -fdelete-null-pointer-checks"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [duplicated-cond])
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [unused-const-variable])
           fi
           #
           dnl Only gcc 7 or later
           if test "$compiler_num" -ge "700"; then
-            tmp_CFLAGS="$tmp_CFLAGS -Wduplicated-branches"
-            tmp_CFLAGS="$tmp_CFLAGS -Wrestrict"
-            tmp_CFLAGS="$tmp_CFLAGS -Walloc-zero"
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [duplicated-branches])
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [restrict])
+            CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [alloc-zero])
             tmp_CFLAGS="$tmp_CFLAGS -Wformat-overflow=2"
             tmp_CFLAGS="$tmp_CFLAGS -Wformat-truncation=2"
             tmp_CFLAGS="$tmp_CFLAGS -Wimplicit-fallthrough=4"
@@ -1214,11 +1219,11 @@ AC_DEFUN([CURL_SET_COMPILER_WARNING_OPTS], [
         #
         if test "$want_warnings" = "yes"; then
           dnl Activate all warnings
-          tmp_CFLAGS="$tmp_CFLAGS -Wall"
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [all])
           dnl Make string constants be of type const char *
-          tmp_CFLAGS="$tmp_CFLAGS -Wwrite-strings"
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [write-strings])
           dnl Warn use of unsupported GCC features ignored by TCC
-          tmp_CFLAGS="$tmp_CFLAGS -Wunsupported"
+          CURL_ADD_COMPILER_WARNINGS([tmp_CFLAGS], [unsupported])
         fi
         ;;
         #
@@ -1645,3 +1650,24 @@ AC_DEFUN([CURL_VAR_STRIP], [
   [$1]="$ac_var_stripped"
   squeeze [$1]
 ])
+
+dnl CURL_ADD_COMPILER_WARNINGS (WARNING-LIST, NEW-WARNINGS)
+dnl -------------------------------------------------------
+dnl Contents of variable WARNING-LIST and NEW-WARNINGS are
+dnl handled as whitespace separated lists of words.
+dnl Add each compiler warning from NEW-WARNINGS that has not
+dnl been disabled via CFLAGS to WARNING-LIST.
+
+AC_DEFUN([CURL_ADD_COMPILER_WARNINGS], [
+  AC_REQUIRE([CURL_SHFUNC_SQUEEZE])dnl
+  ac_var_added_warnings=""
+  for warning in [$2]; do
+    CURL_VAR_MATCH(CFLAGS, [-Wno-$warning -W$warning])
+    if test "$ac_var_match_word" = "no"; then
+      ac_var_added_warnings="$ac_var_added_warnings -W$warning"
+    fi
+  done
+  dnl squeeze whitespace out of result
+  [$1]="$[$1] $ac_var_added_warnings"
+  squeeze [$1]
+])