diff --git a/0001-Adapt-o3tl-span-to-P1872R0.patch b/0001-Adapt-o3tl-span-to-P1872R0.patch
new file mode 100644
index 0000000..f3aff3d
--- /dev/null
+++ b/0001-Adapt-o3tl-span-to-P1872R0.patch
@@ -0,0 +1,187 @@
+From 8e6865188242bccb3d8aa857ddc990d72a058d3d Mon Sep 17 00:00:00 2001
+From: Stephan Bergmann <sbergman@redhat.com>
+Date: Fri, 6 Dec 2019 16:36:01 +0100
+Subject: [PATCH] Adapt o3tl::span to P1872R0
+
+..."span should have size_type, not index_type"
+(<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1872r0.pdf>), as
+implemented by libc++ since <https://github.com/llvm/llvm-project/commit/
+1466335cf4b2854a0be1defcf279fe50772bad6f> "[libc++][P1872] span should have
+size_type, not index_type."
+
+All uses of index_type had been added to mitigate the previous std::span change
+from signed (ptrdiff_t) to unsigned (size_t) index_type, see
+6ef8420fdbf8dff16de13147c5ab833bc5e01121 "Adapt o3tl::span to updated C++2a
+std::span".  There is no easy solution to transparently support all three
+std::span variants currently out there (signed index_type, unsigned index_type,
+unsigned size_type), without causing compilation failures due to
+CPPUNIT_ASSERT_EQUAL with arguments of different types, or compiler warnings
+about mixed signed/unsigned comparisons.  So rule out the oldest std::span
+variant (signed index_type) in configure.ac (so that o3tl::span will use its
+own hand-rolled code in that case) and simplify the uses of index_type to
+std::size_t (as had already been mentioned in
+6ef8420fdbf8dff16de13147c5ab833bc5e01121).
+
+Change-Id: I6ddf424ffb7941da3f69ad66fd29ecd35f09afae
+Reviewed-on: https://gerrit.libreoffice.org/84652
+Tested-by: Jenkins
+Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
+---
+ config_host/config_global.h.in   |  3 +++
+ configure.ac                     | 16 ++++++++++++++++
+ include/o3tl/span.hxx            | 14 ++++++++------
+ o3tl/qa/test-span.cxx            |  7 ++++---
+ sfx2/source/control/dispatch.cxx |  3 ++-
+ 5 files changed, 33 insertions(+), 10 deletions(-)
+
+diff --git a/config_host/config_global.h.in b/config_host/config_global.h.in
+index adb36c39ab8b..5b04594c12f5 100644
+--- a/config_host/config_global.h.in
++++ b/config_host/config_global.h.in
+@@ -29,6 +29,9 @@ Any change in this header will cause a rebuild of almost everything.
+ // constexpr", and <https://wg21.link/P1143R2> "Adding the constinit keyword":
+ #define HAVE_CPP_CONSTINIT_SORTED_VECTOR 0
+ 
++// Useable C++2a <span>:
++#define HAVE_CPP_SPAN 0
++
+ /* GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87150> "move ctor wrongly chosen in return
+    stmt (derived vs. base)": */
+ #define HAVE_GCC_BUG_87150 0
+diff --git a/configure.ac b/configure.ac
+index 651e9d60c2d4..194a3cc80fa5 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -6701,6 +6701,22 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+ CXXFLAGS=$save_CXXFLAGS
+ AC_LANG_POP([C++])
+ 
++AC_MSG_CHECKING([whether $CXX_BASE supports C++2a <span> with unsigned size_type])
++AC_LANG_PUSH([C++])
++save_CXXFLAGS=$CXXFLAGS
++CXXFLAGS="$CXXFLAGS $CXXFLAGS_CXX11"
++AC_COMPILE_IFELSE([AC_LANG_SOURCE([
++        #include <span>
++        #include <type_traits>
++        // Don't check size_type directly, as it was called index_type before P1872R0:
++        void f(std::span<int> s) { static_assert(std::is_unsigned_v<decltype(s.size())>); };
++    ])], [
++        AC_DEFINE([HAVE_CPP_SPAN],[1])
++        AC_MSG_RESULT([yes])
++    ], [AC_MSG_RESULT([no])])
++CXXFLAGS=$save_CXXFLAGS
++AC_LANG_POP([C++])
++
+ AC_MSG_CHECKING([whether $CXX_BASE has GCC bug 87150])
+ AC_LANG_PUSH([C++])
+ save_CXXFLAGS=$CXXFLAGS
+diff --git a/include/o3tl/span.hxx b/include/o3tl/span.hxx
+index 1618b86df897..b19d2d847ac7 100644
+--- a/include/o3tl/span.hxx
++++ b/include/o3tl/span.hxx
+@@ -12,7 +12,9 @@
+ 
+ #include <sal/config.h>
+ 
+-#if __has_include(<span>)
++#include <config_global.h>
++
++#if HAVE_CPP_SPAN
+ 
+ #include <span>
+ 
+@@ -40,7 +42,7 @@ public:
+     using iterator = pointer;
+     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+     using reverse_iterator = std::reverse_iterator<iterator>;
+-    using index_type = std::size_t;
++    using size_type = std::size_t;
+     using difference_type = std::ptrdiff_t;
+ 
+     constexpr span() noexcept : data_(nullptr), size_(0) {}
+@@ -48,7 +50,7 @@ public:
+     template<std::size_t N>
+     constexpr span (T (&a)[N]) noexcept : data_(a), size_(N) {}
+ 
+-    constexpr span (T *a, index_type len) noexcept
++    constexpr span (T *a, size_type len) noexcept
+         : data_(a), size_(len)
+     {
+         // not terribly sure about this, might need to strengthen it
+@@ -72,9 +74,9 @@ public:
+     { return rbegin(); }
+     constexpr const_reverse_iterator crend() const noexcept { return rend(); }
+ 
+-    constexpr index_type size() const noexcept { return size_; }
++    constexpr size_type size() const noexcept { return size_; }
+ 
+-    constexpr reference operator [](index_type pos) const {
++    constexpr reference operator [](size_type pos) const {
+         assert(pos < size());
+         return data_[pos];
+     }
+@@ -83,7 +85,7 @@ public:
+ 
+ private:
+     pointer    data_;
+-    index_type size_;
++    size_type size_;
+ };
+ 
+ } // namespace o3tl
+diff --git a/o3tl/qa/test-span.cxx b/o3tl/qa/test-span.cxx
+index 7ec67fa7fd91..3cb78ace1db2 100644
+--- a/o3tl/qa/test-span.cxx
++++ b/o3tl/qa/test-span.cxx
+@@ -9,6 +9,7 @@
+ 
+ #include <sal/config.h>
+ 
++#include <cstddef>
+ #include <utility>
+ 
+ #include <cppunit/TestAssert.h>
+@@ -42,7 +43,7 @@ private:
+         CPPUNIT_ASSERT_EQUAL(3, *v.crbegin());
+         CPPUNIT_ASSERT_EQUAL(
+             o3tl::span<int>::difference_type(3), v.crend() - v.crbegin());
+-        CPPUNIT_ASSERT_EQUAL(o3tl::span<int>::index_type(3), v.size());
++        CPPUNIT_ASSERT_EQUAL(std::size_t(3), v.size());
+         CPPUNIT_ASSERT(!v.empty());
+         CPPUNIT_ASSERT_EQUAL(2, v[1]);
+         CPPUNIT_ASSERT_EQUAL(1, *v.data());
+@@ -52,8 +53,8 @@ private:
+             o3tl::span<int const> v1( d1 );
+             o3tl::span<int const> v2( d2 );
+             std::swap(v1, v2);
+-            CPPUNIT_ASSERT_EQUAL(o3tl::span<int>::index_type(4), v1.size());
+-            CPPUNIT_ASSERT_EQUAL(o3tl::span<int>::index_type(2), v2.size());
++            CPPUNIT_ASSERT_EQUAL(std::size_t(4), v1.size());
++            CPPUNIT_ASSERT_EQUAL(std::size_t(2), v2.size());
+         }
+     }
+ };
+diff --git a/sfx2/source/control/dispatch.cxx b/sfx2/source/control/dispatch.cxx
+index 9edf43c4ecd6..9b6519ca1814 100644
+--- a/sfx2/source/control/dispatch.cxx
++++ b/sfx2/source/control/dispatch.cxx
+@@ -20,6 +20,7 @@
+ #include <config_feature_desktop.h>
+ 
+ #include <algorithm>
++#include <cstddef>
+ #include <deque>
+ #include <vector>
+ 
+@@ -1453,7 +1454,7 @@ void SfxDispatcher::SetSlotFilter(SfxSlotFilterState nEnable,
+ {
+ #ifdef DBG_UTIL
+     // Check Array
+-    for ( o3tl::span<sal_uInt16 const>::index_type n = 1; n < pSIDs.size(); ++n )
++    for ( std::size_t n = 1; n < pSIDs.size(); ++n )
+         DBG_ASSERT( pSIDs[n] > pSIDs[n-1], "SetSlotFilter: SIDs not sorted" );
+ #endif
+ 
+-- 
+2.24.1
+
diff --git a/libreoffice.spec b/libreoffice.spec
index 52618aa..d7f0165 100644
--- a/libreoffice.spec
+++ b/libreoffice.spec
@@ -248,6 +248,7 @@ Patch3: 0001-fix-detecting-qrcodegen.patch
 Patch4: 0001-Fix-build-with-poppler-0.83.patch
 Patch5: 0001-Adapt-SAL_WARN-to-C-20-deleted-ostream-for-sal_Unico.patch
 Patch6: 0001-Adapt-to-C-20-deleted-ostream-for-sal_Unicode-aka-ch.patch
+Patch7: 0001-Adapt-o3tl-span-to-P1872R0.patch
 
 %if 0%{?rhel}
 # not upstreamed