diff --git a/configure.ac b/configure.ac
index f58091cc..132c344c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -806,7 +806,7 @@ if test "x$CONFIG_ECMASCRIPT_SMJS" = xyes ||
 	AC_SUBST(SPIDERMONKEY_CFLAGS)
 	AC_SUBST(CONFIG_SPIDERMONKEY)
 	AC_SUBST(CONFIG_XML)
-	CFLAGS="$CFLAGS -fpermissive -Wno-sign-compare -std=c++17 $SPIDERMONKEY_CFLAGS"
+	CFLAGS="$CFLAGS -fpermissive -Wno-sign-compare -std=gnu++17 $SPIDERMONKEY_CFLAGS"
 fi
 
 if test "x$CONFIG_QUICKJS" = xyes; then
@@ -814,7 +814,7 @@ if test "x$CONFIG_QUICKJS" = xyes; then
 	EL_CONFIG(CONFIG_QUICKJS, [quickjs])
 	AC_SUBST(CONFIG_QUICKJS)
 	AC_SUBST(CONFIG_XML)
-	CFLAGS="$CFLAGS -fpermissive -Wno-sign-compare -std=c++17"
+	CFLAGS="$CFLAGS -fpermissive -Wno-sign-compare -std=gnu++17"
 fi
 # ===================================================================
 # Check for Guile, optional even if installed.
diff --git a/meson.build b/meson.build
index 39939ce9..30569d43 100644
--- a/meson.build
+++ b/meson.build
@@ -138,7 +138,7 @@ conf_data.set('HAVE_SYS_TIME_H', 1)
 compiler = meson.get_compiler('c')
 
 if conf_data.get('CONFIG_ECMASCRIPT')
-    extracflags = ['-xc++', '-fpermissive', '-Wno-sign-compare', '-std=c++17']
+    extracflags = ['-xc++', '-fpermissive', '-Wno-sign-compare', '-std=gnu++17']
 else
     extracflags = ['-Wc++-compat']
 endif