diff --git a/srcpkgs/giac/patches/pari_2_13.patch b/srcpkgs/giac/patches/pari_2_13.patch
new file mode 100644
index 0000000000..85ee3aca0a
--- /dev/null
+++ b/srcpkgs/giac/patches/pari_2_13.patch
@@ -0,0 +1,16 @@
+change in order to pass chk_fhan4 with pari-2.13
+
+This patch is already upstream in giac > 1.6 so it will be
+removed when we update giac.
+
+--- a/src/pari.cc	2019-11-21 13:40:55.000000000 +0000
++++ b/src/pari.cc	2021-08-11 20:51:39.243502400 +0000
+@@ -88,7 +88,7 @@
+   static map<string,entree *> pari_function_table;
+   static void do_giac_pari_init(long maxprime){
+ #ifdef PARI_DYNAMIC_STACK
+-    long pari_mem_size=512000;
++    long pari_mem_size=1024000;
+ #else
+     long pari_mem_size=64000000;
+ #endif
diff --git a/srcpkgs/giac/template b/srcpkgs/giac/template
index ca95534498..3689027daf 100644
--- a/srcpkgs/giac/template
+++ b/srcpkgs/giac/template
@@ -1,7 +1,7 @@
 # Template file for 'giac'
 pkgname=giac
 version=1.5.0.87
-revision=4
+revision=5
 wrksrc="giac-${version%.*}"
 build_style=gnu-configure
 makedepends="fltk-devel gmp-devel gsl-devel lapack-devel