diff --git a/src/boot/efi/meson.build b/src/boot/efi/meson.build
index e0edbf18a2..299a01b9be 100644
--- a/src/boot/efi/meson.build
+++ b/src/boot/efi/meson.build
@@ -187,7 +187,7 @@ efi_cflags = cc.get_supported_arguments(
         ]
 ) + [
         '-nostdlib',
-        '-std=gnu99',
+        '-std=gnu11',
         '-ffreestanding',
         '-fshort-wchar',
         '-fvisibility=hidden',
diff --git a/src/fundamental/macro-fundamental.h b/src/fundamental/macro-fundamental.h
index 1c198f6ad9..597429dc6c 100644
--- a/src/fundamental/macro-fundamental.h
+++ b/src/fundamental/macro-fundamental.h
@@ -53,7 +53,7 @@
 #define CONCATENATE(x, y) XCONCATENATE(x, y)
 
 #ifdef SD_BOOT
-        void efi_assert(const char *expr, const char *file, unsigned line, const char *function) _noreturn_;
+        _noreturn_ void efi_assert(const char *expr, const char *file, unsigned line, const char *function);
 
         #ifdef NDEBUG
                 #define assert(expr)