diff --git a/var/spack/repos/builtin/packages/geant4/CLHEP-10.03.03.patch b/var/spack/repos/builtin/packages/geant4/geant4-10.3-clhep-cmake.patch
similarity index 100%
rename from var/spack/repos/builtin/packages/geant4/CLHEP-10.03.03.patch
rename to var/spack/repos/builtin/packages/geant4/geant4-10.3-clhep-cmake.patch
diff --git a/var/spack/repos/builtin/packages/geant4/cxx17.patch b/var/spack/repos/builtin/packages/geant4/geant4-10.3-cxx17-cmake.patch
similarity index 100%
rename from var/spack/repos/builtin/packages/geant4/cxx17.patch
rename to var/spack/repos/builtin/packages/geant4/geant4-10.3-cxx17-cmake.patch
diff --git a/var/spack/repos/builtin/packages/geant4/cxx17_geant4_10_0.patch b/var/spack/repos/builtin/packages/geant4/geant4-10.4-cxx17-cmake.patch
similarity index 100%
rename from var/spack/repos/builtin/packages/geant4/cxx17_geant4_10_0.patch
rename to var/spack/repos/builtin/packages/geant4/geant4-10.4-cxx17-cmake.patch
diff --git a/var/spack/repos/builtin/packages/geant4/geant4-10.7-cxx20-g3tog4.patch b/var/spack/repos/builtin/packages/geant4/geant4-10.7-cxx20-g3tog4.patch
new file mode 100644
index 00000000000..6e447684831
--- /dev/null
+++ b/var/spack/repos/builtin/packages/geant4/geant4-10.7-cxx20-g3tog4.patch
@@ -0,0 +1,26 @@
+diff --git a/source/g3tog4/include/G3EleTable.hh b/source/g3tog4/include/G3EleTable.hh
+index 0ab9c4fd566..18c6f73fde6 100644
+--- a/source/g3tog4/include/G3EleTable.hh
++++ b/source/g3tog4/include/G3EleTable.hh
+@@ -56,7 +56,7 @@ public:  // with description
+ private:
+
+   void LoadUp();
+-  G4int parse(G4double& Z, char* name, char* sym, G4double& A); 
++  G4int parse(G4double& Z, char (&name)[20], char (&sym)[3], G4double& A);
+
+ private:
+
+diff --git a/source/g3tog4/src/G3EleTable.cc b/source/g3tog4/src/G3EleTable.cc
+index cecc494b201..a2f3af3d6a2 100644
+--- a/source/g3tog4/src/G3EleTable.cc
++++ b/source/g3tog4/src/G3EleTable.cc
+@@ -64,7 +64,7 @@ G3EleTable::GetEle(G4double Z){
+ }
+
+ G4int 
+-G3EleTable::parse(G4double& Z, char* name, char* sym, G4double& A){ 
++G3EleTable::parse(G4double& Z, char (&name)[20], char (&sym)[3], G4double& A){
+  G4int rc = 0;
+   if (Z>0 && Z <=_MaxEle){
+     G4int z = (G4int) Z-1;
diff --git a/var/spack/repos/builtin/packages/geant4/package.py b/var/spack/repos/builtin/packages/geant4/package.py
index 81b4748eaef..65926854746 100644
--- a/var/spack/repos/builtin/packages/geant4/package.py
+++ b/var/spack/repos/builtin/packages/geant4/package.py
@@ -20,6 +20,7 @@ class Geant4(CMakePackage):
     executables = ["^geant4-config$"]
 
     maintainers("drbenmorgan", "sethrj")
+
     version("11.3.0", sha256="d9d71daff8890a7b5e0e33ea9a65fe6308ad6713000b43ba6705af77078e7ead")
     version("11.2.2", sha256="3a8d98c63fc52578f6ebf166d7dffaec36256a186d57f2520c39790367700c8d")
     version("11.2.1", sha256="76c9093b01128ee2b45a6f4020a1bcb64d2a8141386dea4674b5ae28bcd23293")
@@ -203,29 +204,30 @@ def std_when(values):
             depends_on("qt@5.9:", when="@11.2:")
     conflicts("@:11.1 ^[virtuals=qmake] qt-base", msg="Qt6 not supported before 11.2")
 
+    # CMAKE PROBLEMS #
     # As released, 10.0.4 has inconsistently capitalised filenames
     # in the cmake files; this patch also enables cxxstd 14
     patch("geant4-10.0.4.patch", when="@10.0.4")
-    # Fix member field typo in g4tools wroot
-    # See https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2640
-    patch("columns-11.patch", when="@11:11.2.2")
-    patch("columns-10.patch", when="@10.4:10")
-    # As released, 10.03.03 has issues with respect to using external
-    # CLHEP.
-    patch("CLHEP-10.03.03.patch", level=1, when="@10.3")
     # Build failure on clang 15, ubuntu 22: see Geant4 problem report #2444
     # fixed by ascii-V10-07-03
-    patch("geant4-10.6.patch", level=1, when="@10.0:10.6")
-    # These patches can be applied independent of the cxxstd value?
-    patch("cxx17.patch", when="@10.3 cxxstd=17")
-    patch("cxx17_geant4_10_0.patch", level=1, when="@10.4.0 cxxstd=17")
-    patch("geant4-10.4.3-cxx17-removed-features.patch", level=1, when="@10.4.3 cxxstd=17")
+    patch("geant4-10.6.patch", when="@10.0:10.6")
+    # Enable "17" cxxstd option in CMake (2 different filenames)
+    patch("geant4-10.3-cxx17-cmake.patch", when="@10.3 cxxstd=17")
+    patch("geant4-10.4-cxx17-cmake.patch", when="@10.4:10.4.2 cxxstd=17")
+    # Fix exported cmake: https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2556
+    patch("package-cache.patch", when="@10.7.0:11.1.2^cmake@3.17:")
 
-    # See https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2556
-    patch("package-cache.patch", level=1, when="@10.7.0:11.1.2^cmake@3.17:")
-
-    # Issue with Twisted tubes, see https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2619
-    patch("twisted-tubes.patch", level=1, when="@11.2.0:11.2.2")
+    # BUILD ERRORS #
+    # Fix C++17: add -D_LIBCPP_ENABLE_CXX17_REMOVED_FEATURES C++ flag
+    patch("geant4-10.4.3-cxx17-removed-features.patch", when="@10.4.3 cxxstd=17")
+    # Fix C++20: build error due to removed-in-C++20 `ostream::operator>>(char*)`
+    # (different, simpler approach than upstream Geant4 changes)
+    patch("geant4-10.7-cxx20-g3tog4.patch", when="@:10.7 cxxstd=20")
+    # Fix member field typo in g4tools wroot: https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2640
+    patch("columns-10.patch", when="@10.4:10")
+    patch("columns-11.patch", when="@11:11.2.2")
+    # Fix navigation errors with twisted tubes: https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2619
+    patch("twisted-tubes.patch", when="@11.2.0:11.2.2")
 
     # NVHPC: "thread-local declaration follows non-thread-local declaration"
     conflicts("%nvhpc", when="+threads")