diff -Nru dune-grid-glue-2.7.0/debian/changelog dune-grid-glue-2.7.0/debian/changelog
--- dune-grid-glue-2.7.0/debian/changelog	2020-07-15 10:43:08.000000000 +0000
+++ dune-grid-glue-2.7.0/debian/changelog	2021-01-14 16:08:33.000000000 +0000
@@ -1,3 +1,16 @@
+dune-grid-glue (2.7.0-3build1) hirsute; urgency=medium
+
+  * Rebuild against new dune 2.7.1.
+
+ -- Gianfranco Costamagna <locutusofborg@debian.org>  Thu, 14 Jan 2021 17:08:33 +0100
+
+dune-grid-glue (2.7.0-3) unstable; urgency=medium
+
+  * Use tag that is guaranteed to be valid. (Closes: #966965)
+    + new patch: 0001-use-0-as-tag-in-MPI-to-avoid-too-large-value.patch
+
+ -- Ansgar <ansgar@debian.org>  Sat, 14 Nov 2020 12:29:58 +0100
+
 dune-grid-glue (2.7.0-2) unstable; urgency=medium
 
   * Upload to unstable.
diff -Nru dune-grid-glue-2.7.0/debian/patches/0001-use-0-as-tag-in-MPI-to-avoid-too-large-value.patch dune-grid-glue-2.7.0/debian/patches/0001-use-0-as-tag-in-MPI-to-avoid-too-large-value.patch
--- dune-grid-glue-2.7.0/debian/patches/0001-use-0-as-tag-in-MPI-to-avoid-too-large-value.patch	1970-01-01 00:00:00.000000000 +0000
+++ dune-grid-glue-2.7.0/debian/patches/0001-use-0-as-tag-in-MPI-to-avoid-too-large-value.patch	2020-11-14 11:27:03.000000000 +0000
@@ -0,0 +1,29 @@
+From e307610be43c2bba81fb5e59b21fa55312ea6deb Mon Sep 17 00:00:00 2001
+From: Ansgar Burchardt <Ansgar.Burchardt@tu-dresden.de>
+Date: Wed, 30 Sep 2020 09:59:07 +0200
+Subject: [PATCH] use `0` as tag in MPI to avoid too large value
+
+Some versions of OpenMPI have a lower limit than `12345678`; the MPI
+standard only guarantees values up to at least `32768` are valid.
+
+Closes: #19
+---
+ dune/grid-glue/common/ringcomm.hh | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/dune/grid-glue/common/ringcomm.hh b/dune/grid-glue/common/ringcomm.hh
+index 36ead9c..9bc8876 100644
+--- a/dune/grid-glue/common/ringcomm.hh
++++ b/dune/grid-glue/common/ringcomm.hh
+@@ -221,7 +221,7 @@ namespace Parallel {
+           std::array<MPI_Request,N> requests_send;
+           std::array<MPI_Request,N> requests_recv;
+ 
+-          int tag = 12345678;
++          int tag = 0;
+           Dune::Hybrid::forEach(indices,
+             // [&](auto i){
+             //   MPI_SendVectorInRing(
+-- 
+2.29.2
+
diff -Nru dune-grid-glue-2.7.0/debian/patches/series dune-grid-glue-2.7.0/debian/patches/series
--- dune-grid-glue-2.7.0/debian/patches/series	1970-01-01 00:00:00.000000000 +0000
+++ dune-grid-glue-2.7.0/debian/patches/series	2020-11-14 11:27:03.000000000 +0000
@@ -0,0 +1 @@
+0001-use-0-as-tag-in-MPI-to-avoid-too-large-value.patch