diff --git a/fusee/build_package3.py b/fusee/build_package3.py
index 39cbd6bdd..e196c2e7b 100644
--- a/fusee/build_package3.py
+++ b/fusee/build_package3.py
@@ -52,8 +52,8 @@ def write_kip_meta(f, kip, ofs):
 def write_header(f, all_kips, wb_size, tk_size, xf_size, ex_size, ms_size, fs_size, rb_size, git_revision, major, minor, micro, relstep, s_major, s_minor, s_micro, s_relstep):
     # Unpack kips
     emummc, kips = all_kips
-    # Write reserved0 (previously entrypoint) as infinite loop instruction.
-    f.write(pk('<I', 0xEAFFFFFE))
+    # Write magic as PK31 magic.
+    f.write(b'PK31')
     # Write metadata offset = 0x10
     f.write(pk('<I', 0x20))
     # Write flags
@@ -64,8 +64,8 @@ def write_header(f, all_kips, wb_size, tk_size, xf_size, ex_size, ms_size, fs_si
     f.write(pk('<I', len(KIP_NAMES)))
     # Write reserved1
     f.write(b'\xCC' * 0xC)
-    # Write magic
-    f.write('FSS0')
+    # Write legacy magic
+    f.write(b'FSS0')
     # Write total size
     f.write(pk('<I', 0x800000))
     # Write reserved2
diff --git a/fusee/program/source/fusee_external_package.hpp b/fusee/program/source/fusee_external_package.hpp
index 113e38222..24a6ac8e9 100644
--- a/fusee/program/source/fusee_external_package.hpp
+++ b/fusee/program/source/fusee_external_package.hpp
@@ -42,15 +42,16 @@ namespace ams::nxboot {
     static_assert(sizeof(ExternalPackageKipMeta) == 0x30);
 
     struct ExternalPackageHeader {
-        static constexpr u32 Magic = util::FourCC<'F','S','S','0'>::Code;
+        static constexpr u32 Magic = util::FourCC<'P', 'K', '3', '1'>::Code;
+        static constexpr u32 LegacyMagic = util::FourCC<'F','S','S','0'>::Code;
 
-        u32 reserved0; /* Previously entrypoint. */
+        u32 magic; /* Previously entrypoint. */
         u32 metadata_offset;
         u32 flags;
         u32 meso_size;
         u32 num_kips;
         u32 reserved1[3];
-        u32 magic;
+        u32 legacy_magic;
         u32 total_size;
         u32 reserved2; /* Previously crt0 offset. */
         u32 content_header_offset;