diff --git a/ethosu/vela/debug_database.py b/ethosu/vela/debug_database.py
index 6964808..006348c 100644
--- a/ethosu/vela/debug_database.py
+++ b/ethosu/vela/debug_database.py
@@ -18,38 +18,37 @@
 from typing import Any
 from typing import Dict
 from typing import List
+from typing import Tuple
+from typing import Union
 
 import lxml.etree as xml
 
 from . import numeric_util
 from .operation import Operation
 
-UntypedDict = Dict[Any, Any]
-UntypedList = List[Any]
-
 
 class DebugDatabase:
     NULLREF = -1
     show_warnings = False
 
     SOURCE_TABLE = "source"
-    _sourceUID: UntypedDict = {}
+    _sourceUID: Dict[Any, int] = {}
     _sourceHeaders = ["id", "operator", "kernel_w", "kernel_h", "ofm_w", "ofm_h", "ofm_d"]
-    _sourceTable: UntypedList = []
+    _sourceTable: List[List[Union[float, int, str]]] = []
 
     OPTIMISED_TABLE = "optimised"
-    _optimisedUID: UntypedDict = {}
+    _optimisedUID: Dict[Any, Tuple[int, int]] = {}
     _optimisedHeaders = ["id", "source_id", "operator", "kernel_w", "kernel_h", "ofm_w", "ofm_h", "ofm_d"]
-    _optimisedTable: UntypedList = []
+    _optimisedTable: List[List[Union[float, int, str]]] = []
 
     QUEUE_TABLE = "queue"
     _queueHeaders = ["offset", "cmdstream_id", "optimised_id"]
-    _queueTable: UntypedList = []
+    _queueTable: List[List[int]] = []
 
     STREAM_TABLE = "cmdstream"
-    _streamUID: UntypedDict = {}
+    _streamUID: Dict[Any, int] = {}
     _streamHeaders = ["id", "file_offset"]
-    _streamTable: UntypedList = []
+    _streamTable: List[List[int]] = []
 
     @classmethod
     def add_source(cls, op: Operation):
@@ -58,7 +57,7 @@
         cls._sourceUID[op] = uid
         ofm_shape = numeric_util.full_shape(3, op.outputs[0].shape, 1)
         cls._sourceTable.append(
-            [uid, op.type, op.kernel.width, op.kernel.height, ofm_shape[-2], ofm_shape[-3], ofm_shape[-1]]
+            [uid, str(op.type), op.kernel.width, op.kernel.height, ofm_shape[-2], ofm_shape[-3], ofm_shape[-1]]
         )
 
     @classmethod
@@ -80,7 +79,16 @@
             cls._optimisedUID[op] = (uid, src_uid)
             ofm_shape = numeric_util.full_shape(3, op.outputs[0].shape, 1)
             cls._optimisedTable.append(
-                [uid, src_uid, op.type, op.kernel.width, op.kernel.height, ofm_shape[-2], ofm_shape[-3], ofm_shape[-1]]
+                [
+                    uid,
+                    src_uid,
+                    str(op.type),
+                    op.kernel.width,
+                    op.kernel.height,
+                    ofm_shape[-2],
+                    ofm_shape[-3],
+                    ofm_shape[-1],
+                ]
             )
 
     @classmethod
@@ -91,20 +99,20 @@
         return uid
 
     @classmethod
-    def set_stream_offset(cls, key, file_offset):
+    def set_stream_offset(cls, key, file_offset: int):
         assert key in cls._streamUID
         uid = cls._streamUID[key]
         cls._streamTable.append([uid, file_offset])
 
     @classmethod
-    def add_command(cls, stream_id, offset, op: Operation):
+    def add_command(cls, stream_id: int, offset: int, op: Operation):
         assert stream_id < len(cls._streamUID)
         assert op in cls._optimisedUID, "Optimised operator must exist before code generation"
         optimised_id = cls._optimisedUID[op][0]
         cls._queueTable.append([offset, stream_id, optimised_id])
 
     @classmethod
-    def _write_table(cls, root, name, headers, table):
+    def _write_table(cls, root: xml.Element, name: str, headers: List[str], table):
         # Convert table to CSV
         out = io.StringIO()
         writer = csv.writer(out, quoting=csv.QUOTE_NONNUMERIC)
@@ -116,7 +124,7 @@
         table.text = xml.CDATA(out.getvalue())
 
     @classmethod
-    def write(cls, file_path, input_file, output_file):
+    def write(cls, file_path: str, input_file: str, output_file: str):
         root = xml.Element("debug", {"source": input_file, "optimised": output_file})
 
         cls._write_table(root, cls.SOURCE_TABLE, cls._sourceHeaders, cls._sourceTable)