diff --git a/programs/develop/backy/gcc_version/Tupfile.lua b/programs/develop/backy/gcc_version/Tupfile.lua
index 04d1f445eb..101e756deb 100755
--- a/programs/develop/backy/gcc_version/Tupfile.lua
+++ b/programs/develop/backy/gcc_version/Tupfile.lua
@@ -8,5 +8,7 @@ then CFLAGS = CFLAGS .. " -Dlang_ru"
 else CFLAGS = CFLAGS .. " -Dlang_en"
 end
 
+CFLAGS = CFLAGS .. " -std=c99"
+
 compile_gcc{"Backy.c"}
 link_gcc("Backy")