diff --git a/gguf-py/gguf/gguf.py b/gguf-py/gguf/gguf.py
index a2271d225d001..7e495cb19638d 100644
--- a/gguf-py/gguf/gguf.py
+++ b/gguf-py/gguf/gguf.py
@@ -646,18 +646,17 @@ def get_type(val):
             sys.exit()
 
 
+class WriterState(Enum):
+    EMPTY   = auto()
+    HEADER  = auto()
+    KV_DATA = auto()
+    TI_DATA = auto()
+
+
 class GGUFWriter:
     fout: BufferedWriter
-    arch: str
-    offset_tensor = 0
-    data_alignment = GGUF_DEFAULT_ALIGNMENT
-    kv_data = b""
-    kv_data_count = 0
-    ti_data = b""
-    ti_data_count = 0
-    use_temp_file: bool
-    temp_file: tempfile.SpooledTemporaryFile[bytes] | None = None
-    tensors: list[tuple[np.ndarray[Any, Any], int]]
+    temp_file: tempfile.SpooledTemporaryFile[bytes] | None
+    tensors: list[np.ndarray[Any, Any]]
 
     @property
     def pack_prefix(self):
@@ -683,27 +682,47 @@ def __init__(self, path: os.PathLike[str] | str, arch: str, use_temp_file = True
             GGUFValueType.FLOAT64: f"{self.pack_prefix}d",
             GGUFValueType.BOOL:    "?" ,
         }
-        self.add_architecture()
+        self.offset_tensor = 0
+        self.data_alignment = GGUF_DEFAULT_ALIGNMENT
+        self.kv_data = b""
+        self.kv_data_count = 0
+        self.ti_data = b""
+        self.ti_data_count = 0
         self.use_temp_file = use_temp_file
+        self.temp_file = None
         self.tensors = []
         endianess_str = "Big Endian" if self.endianess == GGUFEndian.BIG else "Little Endian"
         print(f"This gguf file is for {endianess_str} only")
+        self.state = WriterState.EMPTY
+
+        self.add_architecture()
 
     def write_header_to_file(self):
+        if self.state is not WriterState.EMPTY:
+            raise ValueError(f'Expected output file to be empty, got {self.state}')
+
         self.fout.write(struct.pack("<I", GGUF_MAGIC))
         self.fout.write(struct.pack(f"{self.pack_prefix}I", GGUF_VERSION))
         self.fout.write(struct.pack(f"{self.pack_prefix}Q", self.ti_data_count))
         self.fout.write(struct.pack(f"{self.pack_prefix}Q", self.kv_data_count))
         self.flush()
-#        print("tensors " + str(self.ti_data_count) + " kv " + str(self.kv_data_count))
+        self.state = WriterState.HEADER
 
     def write_kv_data_to_file(self):
+        if self.state is not WriterState.HEADER:
+            raise ValueError(f'Expected output file to contain the header, got {self.state}')
+
         self.fout.write(self.kv_data)
         self.flush()
+        self.state = WriterState.KV_DATA
 
     def write_ti_data_to_file(self):
+        if self.state is not WriterState.KV_DATA:
+            raise ValueError(f'Expected output file to contain KV data, got {self.state}')
+
         self.fout.write(self.ti_data)
         self.flush()
+        self.state = WriterState.TI_DATA
 
     def add_key(self, key: str):
         self.add_val(key, GGUFValueType.STRING, add_vtype=False)
@@ -796,6 +815,9 @@ def ggml_pad(x: int, n: int) -> int:
         return ((x + n - 1) // n) * n
 
     def add_tensor_info(self, name: str, tensor_shape: Sequence[int], tensor_dtype: np.dtype[np.float16] | np.dtype[np.float32], tensor_nbytes: int, raw_dtype: GGMLQuantizationType | None = None):
+        if self.state is not WriterState.EMPTY:
+            raise ValueError(f'Expected output file to be empty, got {self.state}')
+
         assert raw_dtype is not None or tensor_dtype in (np.float32, np.float16), "Only F32 and F16 tensors are supported for now"
 
         encoded_name = name.encode("utf8")
@@ -825,23 +847,22 @@ def add_tensor(self, name: str, tensor: np.ndarray[Any, Any], raw_shape: Sequenc
         shape: Sequence[int] = raw_shape if raw_shape is not None else tensor.shape
         self.add_tensor_info(name, shape, tensor.dtype, tensor.nbytes, raw_dtype = raw_dtype)
 
-        pad = GGUFWriter.ggml_pad(tensor.nbytes, self.data_alignment) - tensor.nbytes
-
-        if  self.temp_file is None:
-            self.tensors.append((tensor, pad))
+        if self.temp_file is None:
+            self.tensors.append(tensor)
             return
 
         tensor.tofile(self.temp_file)
+        self.write_padding(self.temp_file, tensor.nbytes)
 
-        if pad != 0:
-            self.temp_file.write(bytes([0] * pad))
-
-    def write_padding(self, fp: BinaryIO, n: int, align: int | None = None):
+    def write_padding(self, fp: IO[bytes], n: int, align: int | None = None):
         pad = GGUFWriter.ggml_pad(n, align if align is not None else self.data_alignment) - n
         if pad != 0:
             fp.write(bytes([0] * pad))
 
     def write_tensor_data(self, tensor: np.ndarray[Any, Any]):
+        if self.state is not WriterState.TI_DATA:
+            raise ValueError(f'Expected output file to contain tensor info, got {self.state}')
+
         if self.endianess==GGUFEndian.BIG:
             tensor.byteswap(inplace=True)
         self.write_padding(self.fout, self.fout.tell())
@@ -854,10 +875,13 @@ def write_tensors_to_file(self):
         self.write_padding(self.fout, self.fout.tell())
 
         if self.temp_file is None:
-            for (currtensor, currpad) in self.tensors:
-                currtensor.tofile(self.fout)
-                if currpad != 0:
-                    self.fout.write(bytes([0] * currpad))
+            while True:
+                try:
+                    tensor = self.tensors.pop(0)
+                except IndexError:
+                    break
+                tensor.tofile(self.fout)
+                self.write_padding(self.fout, tensor.nbytes)
             return
 
         self.temp_file.seek(0)
@@ -1002,11 +1026,8 @@ def add_pad_token_id(self, id: int):
 
 
 class SpecialVocab:
-    load_merges: bool = False
-    merges: list[str] = []
-    special_token_types: tuple[str, ...] = ('bos', 'eos', 'unk', 'sep', 'pad')
-    special_token_ids: dict[str, int] = {}
-    n_vocab: int | None = None
+    merges: list[str]
+    special_token_ids: dict[str, int]
 
     def __init__(
         self, path: str | os.PathLike[str], load_merges: bool = False,
@@ -1016,8 +1037,11 @@ def __init__(
         self.special_token_ids = {}
         self.n_vocab = n_vocab
         self.load_merges = load_merges
+        self.merges = []
         if special_token_types is not None:
             self.special_token_types = special_token_types
+        else:
+            self.special_token_types = ('bos', 'eos', 'unk', 'sep', 'pad')
         self._load(Path(path))
 
     def _load(self, path: Path) -> None:
diff --git a/gguf-py/pyproject.toml b/gguf-py/pyproject.toml
index f0741a7c23e03..c6cb2c37a0e0a 100644
--- a/gguf-py/pyproject.toml
+++ b/gguf-py/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "gguf"
-version = "0.4.5"
+version = "0.4.6"
 description = "Write ML models in GGUF for GGML"
 authors = ["GGML <ggml@ggml.ai>"]
 packages = [