--- Makefile.in.orig	2026-02-04 14:58:05
+++ Makefile.in	2026-02-04 14:58:20
@@ -1252,7 +1252,7 @@
 	uninstall-pkgconfigDATA
 
 fortran/unix.f: fortran/unix.m4 Makefile
-	m4 $(M4_ARG) $< > $@
+	$(M4) $(M4_ARG) $< > $@
 
 # Clean up Fortran modules.
 clean-local: clean-modules