diff --git a/linux/Makefile.am b/linux/Makefile.am
index 0318abef..f35c3d83 100644
--- a/linux/Makefile.am
+++ b/linux/Makefile.am
@@ -326,6 +326,10 @@ ccextractor_CFLAGS += -DPAC_CONFIG_DARWIN -Dfopen64=fopen -Dopen64=open -Dlseek6
 ccextractor_LDADD += -liconv -lz 
 endif
 
+if SYS_IS_64_BIT
+ccextractor_CFLAGS += -DGPAC_64_BITS
+endif
+
 if HARDSUBX_IS_ENABLED
 ccextractor_CFLAGS += -DENABLE_HARDSUBX
 ccextractor_CPPFLAGS+= ${libavcodec_CFLAGS}
diff --git a/linux/configure.ac b/linux/configure.ac
index 4bcee875..4e68793f 100644
--- a/linux/configure.ac
+++ b/linux/configure.ac
@@ -115,6 +115,7 @@ AM_CONDITIONAL(TESSERACT_PRESENT_RPI, [ test -d "/usr/include/tesseract" && test
 AM_CONDITIONAL(SYS_IS_LINUX, [ test `uname -s` = "Linux"])
 AM_CONDITIONAL(SYS_IS_MAC, [ test `uname -s` = "Darwin"])
 AM_CONDITIONAL(BUILD_WITH_GUI, [test "x$with_gui" = "xyes"])
+AM_CONDITIONAL(SYS_IS_64_BIT,[test `getconf LONG_BIT` = "64"])
 
 AC_CONFIG_FILES([Makefile])
 AC_OUTPUT