diff --git a/Makefile.in b/Makefile.in
index 9962af91..2b6786cd 100755
--- a/Makefile.in
+++ b/Makefile.in
@@ -62,6 +62,7 @@ $(addprefix src/,$(PACKAGES)): src/%: src/original-%
 	cp -R $< $@.tmp
 	$(srcdir)/scripts/cp_s $(srcdir)/$(notdir $@) $@.tmp
 	cd $@.tmp && patch -p1 < $(srcdir)/patches/$(notdir $@)
+	if test -f $@.tmp/contrib/download_prerequisites && test "@NEED_GCC_EXTERNAL_LIBRARIES@" == "true"; then cd $@.tmp && ./contrib/download_prerequisites; fi
 	mv $@.tmp $@
 
 .PHONY: patches $(addprefix $(srcdir)/patches/,$(PACKAGES))
diff --git a/configure.ac b/configure.ac
index 2f2254c5..7059fc13 100644
--- a/configure.ac
+++ b/configure.ac
@@ -18,14 +18,16 @@ AC_PATH_PROGS_FEATURE_CHECK([GSED], [gsed sed],
 	[AC_MSG_ERROR([GNU sed not found])])
 AC_SUBST([GSED], [$ac_cv_path_GSED])
 
-AC_CHECK_LIB(gmp, __gmpz_init, ,
-	[AC_MSG_ERROR([GNU MP not found; see https://gmplib.org/])])
-
-AC_CHECK_LIB(mpfr, mpfr_init, ,
-	[AC_MSG_ERROR([MPFR not found; see http://www.mpfr.org/])])
-
-AC_CHECK_LIB(mpc, mpc_init2, ,
-	[AC_MSG_ERROR([MPC not found; see http://www.multiprecision.org/])])
+need_gcc_external_libraries="no"
+AC_CHECK_LIB(gmp, __gmpz_init,
+        [need_gcc_external_libraries="yes"])
+AC_CHECK_LIB(mpfr, mpfr_init,
+        [need_gcc_external_libraries="yes"])
+AC_CHECK_LIB(mpc, mpc_init2,
+        [need_gcc_external_libraries="yes"])
+AS_IF([test x"$need_gcc_external_libraries" == xno],
+      [AC_SUBST(NEED_GCC_EXTERNAL_LIBRARIES,true)],
+      [AC_SUBST(NEED_GCC_EXTERNAL_LIBRARIES,false)])
 
 AC_PATH_PROG([CURL], [curl], [no])
 AC_PATH_PROG([WGET], [wget], [no])