diff --git a/Makefile b/Makefile
index 151f50e0e6..42e4d41ea1 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ VPATH=$(SRC_PATH)
 
 CFLAGS=$(OPTFLAGS) -I. -I$(SRC_PATH) -I$(SRC_PATH)/libavutil \
        -I$(SRC_PATH)/libavcodec -I$(SRC_PATH)/libavformat \
-       -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_GNU_SOURCE
+       -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_ISOC9X_SOURCE
 LDFLAGS+= -g
 
 MANPAGES=doc/ffmpeg.1
diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 17c1680274..33cdc07bc9 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -6,7 +6,7 @@ include ../config.mak
 
 # NOTE: -I.. is needed to include config.h
 CFLAGS=$(OPTFLAGS) -DHAVE_AV_CONFIG_H -I.. -I$(SRC_PATH)/libavutil \
-       -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_GNU_SOURCE $(AMR_CFLAGS)
+       -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_ISOC9X_SOURCE $(AMR_CFLAGS)
 
 OBJS= bitstream.o utils.o mem.o allcodecs.o \
       mpegvideo.o jrevdct.o jfdctfst.o jfdctint.o\
diff --git a/libavformat/Makefile b/libavformat/Makefile
index e512e24a44..00141e818e 100644
--- a/libavformat/Makefile
+++ b/libavformat/Makefile
@@ -6,7 +6,7 @@ include ../config.mak
 
 CFLAGS=$(OPTFLAGS) -I.. -I$(SRC_PATH) -I$(SRC_PATH)/libavutil \
        -I$(SRC_PATH)/libavcodec -DHAVE_AV_CONFIG_H -D_FILE_OFFSET_BITS=64 \
-       -D_LARGEFILE_SOURCE -D_GNU_SOURCE
+       -D_LARGEFILE_SOURCE -D_ISOC9X_SOURCE
 
 OBJS= utils.o cutils.o os_support.o allformats.o
 CPPOBJS=
diff --git a/libavutil/Makefile b/libavutil/Makefile
index 9870cfb0a1..18acf2c041 100644
--- a/libavutil/Makefile
+++ b/libavutil/Makefile
@@ -5,7 +5,7 @@ include ../config.mak
 
 # NOTE: -I.. is needed to include config.h
 CFLAGS=$(OPTFLAGS) -DHAVE_AV_CONFIG_H -DBUILD_AVUTIL -I.. \
-       -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_GNU_SOURCE
+       -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_ISOC9X_SOURCE
 
 OBJS= mathematics.o \
       rational.o \