diff --git a/mpqc-2.3.1-cpp20-std_istream-redirect.patch b/mpqc-2.3.1-cpp20-std_istream-redirect.patch
new file mode 100644
index 0000000..54c3ab0
--- /dev/null
+++ b/mpqc-2.3.1-cpp20-std_istream-redirect.patch
@@ -0,0 +1,29 @@
+--- mpqc-2.3.1/src/lib/util/state/state_text.cc.cpp20	2002-10-11 04:58:21.000000000 +0900
++++ mpqc-2.3.1/src/lib/util/state/state_text.cc	2026-01-15 14:40:20.392566622 +0900
+@@ -138,6 +138,7 @@ StateInText::no_array()
+ 
+ ///////////////////////////////////////////////////////////////////////
+ 
++/*
+ int
+ StateInText::read(char*s)
+ {
+@@ -149,6 +150,7 @@ StateInText::read(char*s)
+     }
+   return strlen(s)+1;
+ }
++*/
+ 
+ int
+ StateInText::read(unsigned int&i)
+--- mpqc-2.3.1/src/lib/util/state/state_text.h.cpp20	2002-04-03 15:44:40.000000000 +0900
++++ mpqc-2.3.1/src/lib/util/state/state_text.h	2026-01-15 14:40:28.004235129 +0900
+@@ -94,7 +94,7 @@ class StateInText: public StateInFile {
+     void no_newline();
+     void no_array();
+ 
+-    int read(char*);
++    /* int read(char*); */
+     int read(unsigned int&);
+     int read(int&);
+     int read(float&);
diff --git a/mpqc.spec b/mpqc.spec
index 90b57ed..4253eb1 100644
--- a/mpqc.spec
+++ b/mpqc.spec
@@ -1,7 +1,7 @@
 Name:           mpqc
 Summary:        Ab-inito chemistry program
 Version:        2.3.1
-Release:        64%{?dist}
+Release:        66%{?dist}
 # Automatically converted from old format: GPLv2+ and LGPLv2+ - review is highly recommended.
 License:        GPL-2.0-or-later AND LicenseRef-Callaway-LGPLv2+
 URL:            http://www.mpqc.org/
@@ -15,6 +15,8 @@ Patch2:         mpqc-2.3.1-cpp11-constexpr.patch
 Patch3:         mpqc-2.3.1-c23-function-prototype.patch
 # C++17 build fix: remove deprecated exception specification
 Patch4:         mpqc-2.3.1-cpp17-exception-specification.patch
+# C++20 fix: std::istream operator>>(char *) removal
+Patch5:         mpqc-2.3.1-cpp20-std_istream-redirect.patch
 Requires:       %{name}-libs%{?_isa} = %{version}-%{release}
 BuildRequires:  make
 BuildRequires:  gcc-c++
@@ -77,6 +79,7 @@ based on mpqc computational chemistry package from Sandia Labs.
 %patch -P2 -p1 -b .cpp11
 %patch -P3 -p1 -b .c23
 %patch -P4 -p1 -b .cpp17
+%patch -P5 -p1 -b .cpp20
 
 sed -i -e 's,molrender.in,%{_datadir}/molrender/molrender.in,g' src/bin/molrender/tkmolrender.in
 sed -i -e 's,prefix/lib,prefix/%{_lib},g' configure.in
@@ -199,6 +202,12 @@ done
 
 
 %changelog
+* Thu Jan 15 2026 Mamoru TASAKA <mtasaka@fedoraproject.org> - 2.3.1-66
+- c++20 fix for std::istream redirect operator change
+
+* Thu Jul 24 2025 Fedora Release Engineering <releng@fedoraproject.org> - 2.3.1-65
+- Rebuilt for https://fedoraproject.org/wiki/Fedora_43_Mass_Rebuild
+
 * Fri Jan 31 2025 Mamoru TASAKA <mtasaka@fedoraproject.org> - 2.3.1-64
 - Use wish instead of tk for BuildRequires
 - F42: rebuild with wish in tk9