diff --git a/external/libstaroffice/0001-Fix-equality-operator-arguments.patch.1 b/external/libstaroffice/0001-Fix-equality-operator-arguments.patch.1
new file mode 100644
index 000000000000..27fd97727e25
--- /dev/null
+++ b/external/libstaroffice/0001-Fix-equality-operator-arguments.patch.1
@@ -0,0 +1,56 @@
+From 9c0ff663659a28720c4ee3f5752bb8ce8121648f Mon Sep 17 00:00:00 2001
+From: Stephan Bergmann <sbergman@redhat.com>
+Date: Mon, 21 Oct 2019 17:17:48 +0200
+Subject: [PATCH] Fix equality operator arguments
+
+...which avoids overload resolution ambiguities in C++20, when a synthesized
+candidate of operator == for a reversed-argument rewrite conflicts with the
+actual operator ==, as one is a template specialization for int and the other
+for float.  (As observed with recent Clang 10 trunk with -std=c++2a when
+building libstaroffice as part of LibreOffice:
+
+> STOFFChart.cxx:230:63: error: use of overloaded operator '==' is ambiguous (with operand types 'STOFFVec2f' (aka 'STOFFVec2<float>') and 'STOFFVec2i' (aka 'STOFFVec2<int>'))
+>     bool autoPlace=m_legendPosition==STOFFBox2f()||m_dimension==STOFFVec2i();
+>                                                    ~~~~~~~~~~~^ ~~~~~~~~~~~~
+> ./libstaroffice_internal.hxx:687:8: note: candidate function
+>   bool operator==(STOFFVec2<T> const &p) const
+>        ^
+> ./libstaroffice_internal.hxx:687:8: note: candidate function (with reversed parameter order)
+> STOFFChart.cxx:270:63: error: use of overloaded operator '==' is ambiguous (with operand types 'STOFFVec2f' (aka 'STOFFVec2<float>') and 'STOFFVec2i' (aka 'STOFFVec2<int>'))
+>   bool autoPlace=m_plotAreaPosition==STOFFBox2f()||m_dimension==STOFFVec2i();
+>                                                    ~~~~~~~~~~~^ ~~~~~~~~~~~~
+> ./libstaroffice_internal.hxx:687:8: note: candidate function
+>   bool operator==(STOFFVec2<T> const &p) const
+>        ^
+> ./libstaroffice_internal.hxx:687:8: note: candidate function (with reversed parameter order)
+
+)
+---
+ src/lib/STOFFChart.cxx | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/src/lib/STOFFChart.cxx b/src/lib/STOFFChart.cxx
+index 3e7310c..b861762 100644
+--- a/src/lib/STOFFChart.cxx
++++ b/src/lib/STOFFChart.cxx
+@@ -227,7 +227,7 @@ void STOFFChart::sendChart(STOFFSpreadsheetListenerPtr &listener, librevenge::RV
+ 
+   // legend
+   if (m_legend.m_show) {
+-    bool autoPlace=m_legendPosition==STOFFBox2f()||m_dimension==STOFFVec2i();
++    bool autoPlace=m_legendPosition==STOFFBox2f()||m_dimension==STOFFVec2f();
+     style=librevenge::RVNGPropertyList();
+     m_legend.addStyleTo(style);
+     style.insert("librevenge:chart-id", styleId);
+@@ -267,7 +267,7 @@ void STOFFChart::sendChart(STOFFSpreadsheetListenerPtr &listener, librevenge::RV
+   }
+   // plot area
+   style=librevenge::RVNGPropertyList();
+-  bool autoPlace=m_plotAreaPosition==STOFFBox2f()||m_dimension==STOFFVec2i();
++  bool autoPlace=m_plotAreaPosition==STOFFBox2f()||m_dimension==STOFFVec2f();
+   m_plotAreaStyle.addTo(style);
+   style.insert("librevenge:chart-id", styleId);
+   style.insert("chart:include-hidden-cells","false");
+-- 
+2.21.0
+
diff --git a/external/libstaroffice/UnpackedTarball_libstaroffice.mk b/external/libstaroffice/UnpackedTarball_libstaroffice.mk
index f2c9ccc460af..0e51f67625ac 100644
--- a/external/libstaroffice/UnpackedTarball_libstaroffice.mk
+++ b/external/libstaroffice/UnpackedTarball_libstaroffice.mk
@@ -29,8 +29,11 @@ $(eval $(call gb_UnpackedTarball_add_patches,libstaroffice, \
 ))
 endif
 
+# * external/libstaroffice/0001-Fix-equality-operator-arguments.patch.1 is upstream at
+#   <https://github.com/fosnola/libstaroffice/pull/6> "Fix equality operator arguments":
 $(eval $(call gb_UnpackedTarball_add_patches,libstaroffice,\
 	external/libstaroffice/0001-add-missing-include-for-std-max.patch.1 \
+	external/libstaroffice/0001-Fix-equality-operator-arguments.patch.1 \
 ))
 
 # vim: set noet sw=4 ts=4: