diff --git a/sci-mathematics/gfan/files/gfan-0.6.2-gcc15.patch b/sci-mathematics/gfan/files/gfan-0.6.2-gcc15.patch
new file mode 100644
index 0000000000000..3e4b75e292c56
--- /dev/null
+++ b/sci-mathematics/gfan/files/gfan-0.6.2-gcc15.patch
@@ -0,0 +1,22 @@
+https://github.com/Singular/Singular/commit/d3f73432d73ac0dd041
+
+diff --git a/src/gfanlib_matrix.h b/src/gfanlib_matrix.h
+index 418fa4c..27818b2 100644
+--- a/src/gfanlib_matrix.h
++++ b/src/gfanlib_matrix.h
+@@ -115,6 +115,7 @@ public:
+         	  p[i][j]=s*(q[i][j]);
+       return p;
+     }
++  /*
+   friend Matrix operator*(const Matrix& a, const Matrix& b)
+     {
+       assert(a.width==b.height);
+@@ -123,6 +124,7 @@ public:
+         ret[i]=a.vectormultiply(b.column(i));
+       return ret.transposed();
+     }
++  */
+   /*  template<class T>
+     Matrix<T>(const Matrix<T>& c):v(c.size()){
+     for(int i=0;i<size();i++)v[i]=typ(c[i]);}
diff --git a/sci-mathematics/gfan/gfan-0.6.2-r7.ebuild b/sci-mathematics/gfan/gfan-0.6.2-r7.ebuild
new file mode 100644
index 0000000000000..fa24bc6c8dfa0
--- /dev/null
+++ b/sci-mathematics/gfan/gfan-0.6.2-r7.ebuild
@@ -0,0 +1,86 @@
+# Copyright 1999-2025 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=8
+
+inherit flag-o-matic toolchain-funcs
+
+DESCRIPTION="Compute Groebner fans and tropical varieties"
+HOMEPAGE="https://users-math.au.dk/~jensen/software/gfan/gfan.html"
+SRC_URI="https://users-math.au.dk/~jensen/software/${PN}/${PN}${PV}.tar.gz"
+
+S="${WORKDIR}/${PN}${PV}"
+
+LICENSE="GPL-2+"
+SLOT="0"
+KEYWORDS="~amd64 ~arm ~riscv ~x86 ~amd64-linux ~x86-linux"
+IUSE="doc"
+
+# texlive-plaingeneric is needed for \usepackage{ulem} in
+# the manual. ghostscript-gpl provides the "dvipdf" command.
+BDEPEND="doc? (
+	app-text/ghostscript-gpl
+	dev-texlive/texlive-plaingeneric
+	virtual/latex-base
+)"
+DEPEND="dev-libs/gmp:0=[cxx(+)]
+	sci-libs/cddlib:0="
+RDEPEND="${DEPEND}"
+
+PATCHES=(
+	"${FILESDIR}/${PN}-0.6.2-testsuite.patch"
+	"${FILESDIR}/${PN}-0.6.2-Makefile.patch"
+	"${FILESDIR}/${PN}-0.6.2-fix-0602ResultantFanProjection.patch"
+	"${FILESDIR}/${PN}-0.6.2-fix-spelling-errors.patch"
+	"${FILESDIR}/${PN}-0.6.2-find-name.patch"
+	"${FILESDIR}/${PN}-0.6.2-glibcxx-assertions.patch"
+	"${FILESDIR}/${PN}-0.6.2-gcc15.patch"
+)
+
+pkg_setup() {
+	tc-export CC CXX
+
+	# This should really go in cppflags, but that doesn't work with
+	# gfan's hand-written Makefile.
+	append-cxxflags -DNOCDDPREFIX -I"${EPREFIX}"/usr/include/cddlib
+}
+
+src_prepare() {
+	default
+
+	# And this one fails (harmlessly) on x86, bug 818397.
+	rm -r testsuite/0009RenderStairCase || \
+		die "unable to disable test 0009RenderStairCase"
+}
+
+src_configure() {
+	# -Werror=odr
+	# https://bugs.gentoo.org/863044
+	# Only contact method is email. I have sent one detailing the issue.
+	filter-lto
+
+	# The upstream Makefile says that GCC produces bad code with -O3.
+	replace-flags "-O3" "-O2"
+	default
+}
+
+src_compile() {
+	default
+	if use doc; then
+		pushd doc > /dev/null || die
+		# The LaTeX build commands need to be repeated until the
+		# document "stops changing," which is not as easy as it
+		# sounds to detect. Running it twice seems to work here.
+		for iteration in 1 2; do
+			latex manual.tex && \
+				bibtex manual && \
+				dvipdf manual.dvi manual.pdf || die
+		done
+		popd > /dev/null || die
+	fi
+}
+
+src_install() {
+	emake PREFIX="${ED}/usr" install
+	use doc && dodoc doc/manual.pdf
+}