diff --git a/common.mak b/common.mak
index cccd00b23d..575780688c 100644
--- a/common.mak
+++ b/common.mak
@@ -19,7 +19,7 @@ endif
 ALLFFLIBS = avcodec avdevice avfilter avformat avutil postproc swscale
 
 CFLAGS := -DHAVE_AV_CONFIG_H -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE \
-          -D_ISOC9X_SOURCE -I$(BUILD_ROOT_REL) -I$(SRC_PATH) $(OPTFLAGS)
+          -I$(BUILD_ROOT_REL) -I$(SRC_PATH) $(OPTFLAGS)
 
 %.o: %.c
 	$(CC) $(CFLAGS) $(LIBOBJFLAGS) -c -o $@ $<
@@ -116,4 +116,4 @@ $(eval $(RULES))
 
 tests: $(TESTS)
 
--include $(DEPS)
+#-include $(DEPS)
diff --git a/configure b/configure
index c099def04a..cbb31bdf5a 100755
--- a/configure
+++ b/configure
@@ -974,6 +974,7 @@ enable stripping
 vhook="default"
 
 # build settings
+add_cflags '-D_ISOC9X_SOURCE'
 SHFLAGS='-shared -Wl,-soname,$$(@F)'
 VHOOKSHFLAGS='$(SHFLAGS)'
 FFSERVERLDFLAGS=-Wl,-E
@@ -1689,7 +1690,6 @@ check_lib math.h sin -lm
 # test for C99 functions in math.h
 for func in llrint lrint lrintf round roundf; do
     check_exec <<EOF && enable $func || disable $func
-#define _ISOC9X_SOURCE  1
 #include <math.h>
 int main(void) { return ($func(3.999f) > 0)?0:1; }
 EOF