diff --git a/aegisub/libffms/Makefile.am b/aegisub/libffms/Makefile.am
index 2204f3dae..0d3dc0646 100644
--- a/aegisub/libffms/Makefile.am
+++ b/aegisub/libffms/Makefile.am
@@ -2,7 +2,7 @@ AUTOMAKE_OPTIONS = subdir-objects
 
 noinst_LIBRARIES = libffmpegsource_aegisub.a
 
-AM_CPPFLAGS = -Icore -Iinclude -D__UNIX__ -DFFMS_EXPORTS -DHAVE_STRLCPY @LIBAVFORMAT_CFLAGS@ @LIBAVCODEC_CFLAGS@ @LIBSWSCALE_CFLAGS@ @LIBAVUTIL_CFLAGS@ @LIBPOSTPROC_CFLAGS@
+AM_CPPFLAGS = -Icore -Iinclude -D__UNIX__ -DFFMS_EXPORTS -DHAVE_STRLCPY -D__STDC_CONSTANT_MACROS @LIBAVFORMAT_CFLAGS@ @LIBAVCODEC_CFLAGS@ @LIBSWSCALE_CFLAGS@ @LIBAVUTIL_CFLAGS@ @LIBPOSTPROC_CFLAGS@
 
 
 libffmpegsource_aegisub_a_SOURCES = \
diff --git a/aegisub/libffms/wscript b/aegisub/libffms/wscript
index bc0c9e889..3dddeef0c 100644
--- a/aegisub/libffms/wscript
+++ b/aegisub/libffms/wscript
@@ -19,7 +19,7 @@ def build(bld):
     obj = bld.new_task_gen(
         features = 'cc cxx cstaticlib',
         target = 'ffmpegsource_aegisub',
-        defines = 'FFMS_EXPORTS HAVE_STRLCPY',
+        defines = 'FFMS_EXPORTS HAVE_STRLCPY __STDC_CONSTANT_MACROS',
         includes = 'include src/core',
         uselib = 'FFMPEG')