diff --git a/pydra/engine/helpers.py b/pydra/engine/helpers.py
index 4d8e84132..682e7e193 100644
--- a/pydra/engine/helpers.py
+++ b/pydra/engine/helpers.py
@@ -649,12 +649,9 @@ def argstr_formatting(argstr, inputs, value_updates=None):
     if value_updates:
         inputs_dict.update(value_updates)
     # getting all fields that should be formatted, i.e. {field_name}, ...
-    inp_fields = re.findall(r"{\w+}", argstr)
-    inp_fields_float = re.findall(r"{\w+:[0-9.]+f}", argstr)
-    inp_fields += [re.sub(":[0-9.]+f", "", el) for el in inp_fields_float]
+    inp_fields = re.findall(r"{(\w+)(?::[0-9.]+f|\[[\w]+\])?}", argstr)
     val_dict = {}
-    for fld in inp_fields:
-        fld_name = fld[1:-1]  # extracting the name form {field_name}
+    for fld_name in inp_fields:
         fld_value = inputs_dict[fld_name]
         fld_attr = getattr(attrs.fields(type(inputs)), fld_name)
         if fld_value is attr.NOTHING or (
diff --git a/pydra/engine/tests/test_helpers.py b/pydra/engine/tests/test_helpers.py
index 06ce39220..308980acb 100644
--- a/pydra/engine/tests/test_helpers.py
+++ b/pydra/engine/tests/test_helpers.py
@@ -4,6 +4,7 @@
 import random
 import platform
 import pytest
+import attrs
 import cloudpickle as cp
 from unittest.mock import Mock
 from fileformats.generic import Directory, File
@@ -15,9 +16,9 @@
     load_and_run,
     position_sort,
     parse_copyfile,
+    argstr_formatting,
 )
 from ...utils.hash import hash_function
-from .. import helpers_file
 from ..core import Workflow
 
 
@@ -311,3 +312,21 @@ def mock_field(copyfile):
         parse_copyfile(mock_field((1, 2)))
     with pytest.raises(TypeError, match="Unrecognised type for collation copyfile"):
         parse_copyfile(mock_field((Mode.copy, 2)))
+
+
+def test_argstr_formatting():
+    @attrs.define
+    class Inputs:
+        a1_field: str
+        b2_field: float
+        c3_field: dict[str, str]
+        d4_field: list[str]
+
+    inputs = Inputs("1", 2.0, {"c": "3"}, ["4"])
+    assert (
+        argstr_formatting(
+            "{a1_field} {b2_field:02f} -test {c3_field[c]} -me {d4_field[0]}",
+            inputs,
+        )
+        == "1 2.000000 -test 3 -me 4"
+    )