diff --git a/overlay.nix b/overlay.nix
index 972c842..2f973f3 100644
--- a/overlay.nix
+++ b/overlay.nix
@@ -10,4 +10,12 @@ final: prev:
         # Check with: riscv64-unknown-elf-objdump -d -M no-aliases rotate
     ];
   });
+
+  # Fix GCC 13 format-overflow warning/error:
+  # ../src/shared/install.c:444:64: error: ‘%s’ directive argument is null [-Werror=format-overflow=]
+  # 444 |                         err = log_error_errno(changes[i].type, "Failed to %s unit, unit %s does not exist.",
+  #     |                                                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  systemd = prev.systemd.overrideAttrs (old: {
+    CFLAGS = "-Wno-error=format-overflow";
+  });
 }