diff --git a/pkgs/games/wesnoth/default.nix b/pkgs/games/wesnoth/default.nix
index 1e058c39481b..6f894432e572 100644
--- a/pkgs/games/wesnoth/default.nix
+++ b/pkgs/games/wesnoth/default.nix
@@ -21,6 +21,7 @@
   icu,
   lua,
   curl,
+  fetchpatch,
 }:
 
 stdenv.mkDerivation rec {
@@ -34,6 +35,33 @@ stdenv.mkDerivation rec {
     hash = "sha256-c3BoTFnSUqtp71QeSCsC2teVuzsQwV8hOJtIcZdP+1E=";
   };
 
+  # LLVM 19 removed support for types not officially supported by `std::char_traits`:
+  # https://libcxx.llvm.org/ReleaseNotes/19.html#deprecations-and-removals
+  # Wesnoth <1.19 relies on this previously supported non-standard behavior for
+  # some types that should either have been a vector or span:
+  # https://github.com/wesnoth/wesnoth/issues/9546
+  # Wesnoth moved to a `std::span` wrapper for byte views in the 1.19 branch, which we apply as
+  # patches until 1.20 is released.
+  patches = lib.optionals (stdenv.cc.isClang && lib.versionAtLeast stdenv.cc.version "19") [
+    # The next two patches are cherry-picked from https://github.com/wesnoth/wesnoth/pull/10102,
+    # which is already included in the 1.19 branch.
+    # Introduces the `std::span` wrapper based on `boost::span`.
+    (fetchpatch {
+      url = "https://github.com/wesnoth/wesnoth/commit/63266cc2c88fefa7e0792ac59d14c14e3711440c.patch";
+      hash = "sha256-3Zi/njG7Kovmyd7yiKUoeu4u0QPQxxw+uLz+k9isOLU=";
+    })
+    # Replace all string views with spans.
+    (fetchpatch {
+      url = "https://github.com/wesnoth/wesnoth/commit/d3daa161eb2c02670b5ffbcf86cd0ec787f6b9ee.patch";
+      hash = "sha256-9DCeZQZKE6fN91T5DCpNJsKGXbv5ihZC8UpuNkiA9zc=";
+    })
+    # Wesnoth <1.19 uses `std::basic_string` for lightmap computations, which is not standard compliant
+    # and incompatible to LLVM 19.
+    # While this was fixed in https://github.com/wesnoth/wesnoth/pull/10128, the fix is not
+    # trivially backportable to 1.18 so we apply a simpler fix instead.
+    ./llvm19-lightmap.patch
+  ];
+
   nativeBuildInputs = [
     cmake
     pkg-config
diff --git a/pkgs/games/wesnoth/llvm19-lightmap.patch b/pkgs/games/wesnoth/llvm19-lightmap.patch
new file mode 100644
index 000000000000..34edc173ff0c
--- /dev/null
+++ b/pkgs/games/wesnoth/llvm19-lightmap.patch
@@ -0,0 +1,59 @@
+diff --git a/src/display.cpp b/src/display.cpp
+index 0f6552222b7..9d50046de2f 100644
+--- a/src/display.cpp
++++ b/src/display.cpp
+@@ -1082,7 +1082,8 @@ void display::get_terrain_images(const map_location& loc, const std::string& tim
+
+ 		// add the directional transitions
+ 		tod_color acol = atod1.color + color_adjust_;
+-		lt += image::get_light_string(d + 1, acol.r, acol.g, acol.b);
++		auto new_lt = image::get_light_string(d + 1, acol.r, acol.g, acol.b);
++		lt.insert(lt.end(), new_lt.begin(), new_lt.end());
+ 	}
+
+ 	for(int d = 0; d < 6; ++d) {
+@@ -1114,7 +1115,8 @@ void display::get_terrain_images(const map_location& loc, const std::string& tim
+
+ 		// add the directional transitions
+ 		tod_color acol = atod1.color + color_adjust_;
+-		lt += image::get_light_string(d + 7, acol.r, acol.g, acol.b);
++		auto new_lt = image::get_light_string(d + 7, acol.r, acol.g, acol.b);
++		lt.insert(lt.end(), new_lt.begin(), new_lt.end());
+ 	}
+
+ 	for(int d = 0; d < 6; ++d) {
+@@ -1146,7 +1148,8 @@ void display::get_terrain_images(const map_location& loc, const std::string& tim
+
+ 		// add the directional transitions
+ 		tod_color acol = atod2.color + color_adjust_;
+-		lt += image::get_light_string(d + 13, acol.r, acol.g, acol.b);
++		auto new_lt = image::get_light_string(d + 13, acol.r, acol.g, acol.b);
++		lt.insert(lt.end(), new_lt.begin(), new_lt.end());
+ 	}
+
+ 	if(lt.empty()){
+diff --git a/src/picture.cpp b/src/picture.cpp
+index e7aeddaa821..5ad1ebcbcbc 100644
+--- a/src/picture.cpp
++++ b/src/picture.cpp
+@@ -526,7 +526,9 @@ static surface apply_light(surface surf, const light_string& ls)
+
+ 		// decompose into atomic lightmap operations (4 chars)
+ 		for(std::size_t c = 0; c + 3 < ls.size(); c += 4) {
+-			light_string sls = ls.substr(c, 4);
++			auto start = ls.begin() + c;
++			auto end = start + 4;
++			light_string sls(start, end);
+
+ 			// get the corresponding image and apply the lightmap operation to it
+ 			// This allows to also cache lightmap parts.
+diff --git a/src/picture.hpp b/src/picture.hpp
+index 85a3b3a15a1..a26e1e27bc7 100644
+--- a/src/picture.hpp
++++ b/src/picture.hpp
+@@ -120,7 +120,7 @@ std::ostream& operator<<(std::ostream&, const locator&);
+  *  7-12: convex half-corners 1
+  * 13-19: convex half-corners 2
+  */
+-typedef std::basic_string<signed char> light_string;
++typedef std::vector<signed char> light_string;