diff --git a/libswscale/Makefile b/libswscale/Makefile
index f75b791d1e9fdefa27cedcfb3087167421c96294..ae667cb1119b74f852855c694df5971d48efde71 100644
--- a/libswscale/Makefile
+++ b/libswscale/Makefile
@@ -10,7 +10,7 @@ endif
 # NOTE: -I.. is needed to include config.h
 CFLAGS=-I.. -I$(SRC_PATH) -I$(SRC_PATH)/libavutil $(OPTFLAGS) \
        -DHAVE_AV_CONFIG_H -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE \
-       -D_GNU_SOURCE
+       -D_ISOC9X_SOURCE
 
 OBJS= swscale.o rgb2rgb.o yuv2rgb.o
 ifeq ($(TARGET_ALTIVEC),yes)