Index: flex-2.5.31/main.c
===================================================================
--- flex-2.5.31.orig/main.c
+++ flex-2.5.31/main.c
@@ -344,7 +344,7 @@ void check_options ()
 
     /* Setup the filter chain. */
     output_chain = filter_create_int(NULL, filter_tee_header, headerfilename);
-    filter_create_ext(output_chain,"m4","-P",0);
+    filter_create_ext(output_chain,GM4_PROGRAM,"-P",0);
     filter_create_int(output_chain, filter_fix_linedirs, NULL);
 
     /* For debugging, only run the requested number of filters. */
Index: flex-2.5.31/Makefile.am
===================================================================
--- flex-2.5.31.orig/Makefile.am
+++ flex-2.5.31/Makefile.am
@@ -141,7 +141,7 @@ SUBDIRS = \
 	tests
 
 localedir = $(datadir)/locale
-AM_CPPFLAGS = -DLOCALEDIR=\"$(localedir)\" -I@includedir@ -I$(top_srcdir)/intl
+AM_CPPFLAGS = -DLOCALEDIR=\"$(localedir)\" -I@includedir@ -I$(top_srcdir)/intl -DGM4_PROGRAM=\"@M4@\"
 LIBS = @LIBINTL@ @LIBS@
 
 skel.c: flex.skl mkskel.sh flexint.h tables_shared.h
Index: flex-2.5.31/Makefile.in
===================================================================
--- flex-2.5.31.orig/Makefile.in
+++ flex-2.5.31/Makefile.in
@@ -290,7 +290,7 @@ SUBDIRS = \
 
 
 localedir = $(datadir)/locale
-AM_CPPFLAGS = -DLOCALEDIR=\"$(localedir)\" -I@includedir@ -I$(top_srcdir)/intl
+AM_CPPFLAGS = -DLOCALEDIR=\"$(localedir)\" -I@includedir@ -I$(top_srcdir)/intl -DGM4_PROGRAM=\"@M4@\"
 
 # Run GNU indent on sources. Don't run this unless all the sources compile cleanly.
 #