diff --git a/pkgs/by-name/gr/grantlee/Fix-cpp-20-build.patch b/pkgs/by-name/gr/grantlee/Fix-cpp-20-build.patch
new file mode 100644
index 000000000000..ebf83a1c5f44
--- /dev/null
+++ b/pkgs/by-name/gr/grantlee/Fix-cpp-20-build.patch
@@ -0,0 +1,26 @@
+From 261bfe75d718abfc537ddcebfe805df01c33ab3a Mon Sep 17 00:00:00 2001
+From: Pino Toscano <toscano.pino@tiscali.it>
+Date: Sat, 25 Apr 2026 10:21:47 +0200
+Subject: [PATCH] Remove template-id in constructor of template class
+
+It was not required, and it is invalid now in C++ 20.
+---
+ templates/defaulttags/cycle.h | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/templates/defaulttags/cycle.h b/templates/defaulttags/cycle.h
+index 936c2a2e..a917555f 100644
+--- a/templates/defaulttags/cycle.h
++++ b/templates/defaulttags/cycle.h
+@@ -40,9 +40,9 @@ Cycles endlessly over elements.
+ template <typename T> class RingIterator
+ {
+ public:
+-  RingIterator<T>() {}
++  RingIterator() {}
+ 
+-  RingIterator<T>(const QList<T> &list)
++  RingIterator(const QList<T> &list)
+       : m_begin(list.constBegin()), m_it(list.constBegin()),
+         m_end(list.constEnd())
+   {
diff --git a/pkgs/by-name/gr/grantlee/package.nix b/pkgs/by-name/gr/grantlee/package.nix
index fac0814c1492..23ce6dd3f565 100644
--- a/pkgs/by-name/gr/grantlee/package.nix
+++ b/pkgs/by-name/gr/grantlee/package.nix
@@ -2,6 +2,7 @@
   lib,
   stdenv,
   fetchFromGitHub,
+  fetchpatch,
   qt5,
   cmake,
 }:
@@ -30,6 +31,8 @@ stdenv.mkDerivation rec {
   patches = [
     ./grantlee-nix-profiles.patch
     ./grantlee-no-canonicalize-filepath.patch
+    # https://github.com/steveire/grantlee/pull/93
+    ./Fix-cpp-20-build.patch
   ];
 
   outputs = [