diff -rupN postgis-3.1.1/configure.ac postgis-3.1.1-new/configure.ac
--- postgis-3.1.1/configure.ac	2021-01-28 20:10:31.000000000 +0100
+++ postgis-3.1.1-new/configure.ac	2021-03-08 16:36:09.677099539 +0100
@@ -902,7 +902,7 @@ AC_SUBST([PROJ_LDFLAGS])
 dnl Ensure we can link against libproj
 LIBS_SAVE="$LIBS"
 LIBS="$PROJ_LDFLAGS"
-AC_CHECK_LIB([proj], [pj_get_release],
+AC_CHECK_LIB([proj], [proj_info],
 	[],
 	[AC_MSG_ERROR([could not find libproj - you may need to specify the directory of a PROJ installation using --with-projdir])],
 	[])