diff --git a/src/kyupy/vcd.py b/src/kyupy/vcd.py
index 5e2839f..97e1501 100644
--- a/src/kyupy/vcd.py
+++ b/src/kyupy/vcd.py
@@ -154,12 +154,13 @@ GRAMMAR = r"""
     """
 
 
-def load(file, var_locs = lambda _: [], step_filter = lambda *_: True):
+def load(file, var_locs = lambda _: [], step_filter = lambda *_: True, s_len = None):
     """Parses the contents of ``file`` as Verilog Change Dump (VCD).
 
     :param file: A file name or a file handle. Files with `.gz`-suffix are decompressed on-the-fly.
     :param var_locs: A callback ``(var) -> list[int]`` mapping each variable to ndarray column indices. Empty list drops the variable.
     :param step_filter: A callback ``(time, values, var_map) -> bool`` to select which timesteps to include.
+    :param s_len: length of the first axis of returned pattern data.
     :return: A VcdData object with metadata and an ndarray with all values.
     """
     vcd = readtext(file)
@@ -169,10 +170,11 @@ def load(file, var_locs = lambda _: [], step_filter = lambda *_: True):
     vcd_header : VcdHeader = Lark(GRAMMAR, parser="lalr", lexer='contextual', transformer=VcdHeaderTransformer()).parse(vcd_header_str) # type: ignore
     vcd_data = vcd[header_size:].splitlines()
     var_map = VcdVarMap(vcd_header, var_locs)
+    width = s_len if s_len is not None else var_map.total_width
 
     chunk_size = 10240
     chunks = []
-    chunk = np.full((chunk_size, var_map.total_width), logic.UNASSIGNED, dtype=np.uint8)
+    chunk = np.full((chunk_size, width), logic.UNASSIGNED, dtype=np.uint8)
 
     _val_map = {'0': logic.ZERO, '1': logic.ONE,
                 'x': logic.UNKNOWN, 'X': logic.UNKNOWN,
@@ -191,7 +193,7 @@ def load(file, var_locs = lambda _: [], step_filter = lambda *_: True):
                 steps.append(current_time)
                 if step_idx >= chunk_size:
                     chunks.append(chunk)
-                    chunk = np.empty((chunk_size, var_map.total_width), dtype=np.uint8)
+                    chunk = np.empty((chunk_size, width), dtype=np.uint8)
                     chunk[0] = chunks[-1][-1]
                     step_idx = 0
                 else: