diff --git a/kubi-shared/src/data.rs b/kubi-shared/src/data.rs
index 45c41e9..919f2dc 100644
--- a/kubi-shared/src/data.rs
+++ b/kubi-shared/src/data.rs
@@ -11,9 +11,13 @@ use anyhow::Result;
 use crate::{block::Block, chunk::{CHUNK_SIZE, BlockDataRef}};
 
 const SECTOR_SIZE: usize = CHUNK_SIZE * CHUNK_SIZE * CHUNK_SIZE * size_of::<Block>();
-const RESERVED_SIZE: usize = 524288; //512kb (16 sectors assuming 32x32x32 world of 1byte blocks)
+const RESERVED_SIZE: usize = 1048576; //~1mb (16 sectors assuming 32x32x32 world of 1byte blocks)
 const RESERVED_SECTOR_COUNT: usize = RESERVED_SIZE / SECTOR_SIZE;
 
+//magic = "KUBI" + IDENTITY (4 bytes)
+const HEADER_MAGIC_SIZE: usize = 8;
+const HEADER_MAGIC_STR: [u8; 4] = *b"KUBI";
+const HEADER_MAGIC_IDENTITY: u32 = 1;
 
 // #[repr(transparent)]
 // struct IVec2Hash(IVec2);
@@ -22,7 +26,7 @@ struct WorldSaveDataHeader {
   pub name: Cow<'static, str>,
   pub seed: u64,
   sector_count: u32,
-  chunk_map: HashMap<IVec2, u32>
+  chunk_map: HashMap<IVec2, u32>,
 }
 
 impl Default for WorldSaveDataHeader {
@@ -51,13 +55,29 @@ impl WorldSaveFile {
 
   fn read_header(&mut self) -> Result<()> {
     self.file.rewind()?;
-    self.header = bincode::deserialize_from((&self.file).take(RESERVED_SIZE as u64))?;
+
+    let mut subheader = [0u8; HEADER_MAGIC_SIZE];
+    self.file.read_exact(&mut subheader)?;
+    if subheader[0..4] != HEADER_MAGIC_STR {
+      return Err(anyhow::anyhow!("invalid file header"));
+    }
+    if subheader[4..8] != HEADER_MAGIC_IDENTITY.to_be_bytes() {
+      return Err(anyhow::anyhow!("this save file cannot be loaded by this version of the game"));
+    }
+
+    let limit = (RESERVED_SIZE - HEADER_MAGIC_SIZE) as u64;
+    self.header = bincode::deserialize_from((&self.file).take(limit))?;
+
     Ok(())
   }
 
   fn write_header(&mut self) -> Result<()> {
     self.file.rewind()?;
-    ///XXX: this can cause the header to destroy chunk data (if it's WAY too long)
+    self.file.write_all(&HEADER_MAGIC_STR)?;
+    self.file.write_all(&HEADER_MAGIC_IDENTITY.to_be_bytes())?;
+    //XXX: this can cause the header to destroy chunk data (if it's WAY too long)
+    //     read has checks against this, but write doesn't
+    //     1mb is pretty generous tho, so it's not a *big* deal
     bincode::serialize_into(&self.file, &self.header)?;
     Ok(())
   }