diff --git a/dltype/_lib/_parser.py b/dltype/_lib/_parser.py
index f243255..1149558 100644
--- a/dltype/_lib/_parser.py
+++ b/dltype/_lib/_parser.py
@@ -3,7 +3,9 @@
 from __future__ import annotations
 
 import enum
+import itertools
 import logging
+import math
 import re
 from typing import Final
 
@@ -35,6 +37,13 @@ class _DLTypeOperator(enum.Enum):
     DIV = "/"
     MIN = "min"
     MAX = "max"
+    ISQRT = "isqrt"
+
+    def evaluate_unary(self, a: int) -> int:
+        """Evaluate the unary operator."""
+        if self is _DLTypeOperator.ISQRT:
+            return math.isqrt(a)
+        raise NotImplementedError(self)
 
     def evaluate(self, a: int, b: int) -> int:  # noqa: PLR0911
         """Evaluate the operator."""
@@ -63,9 +72,12 @@ def evaluate(self, a: int, b: int) -> int:  # noqa: PLR0911
     _DLTypeOperator.EXP: 3,
     _DLTypeOperator.MIN: 0,
     _DLTypeOperator.MAX: 0,
+    _DLTypeOperator.ISQRT: 0,
 }
 
-_functional_operators: Final = frozenset({_DLTypeOperator.MIN, _DLTypeOperator.MAX})
+_unary_operators: Final = frozenset({_DLTypeOperator.ISQRT})
+_binary_operators: Final = frozenset({_DLTypeOperator.MIN, _DLTypeOperator.MAX})
+_functional_operators: Final = frozenset(_unary_operators.union(_binary_operators))
 _valid_operators: frozenset[str] = frozenset(
     {op.value for op in _DLTypeOperator if op not in _functional_operators},
 )
@@ -174,6 +186,9 @@ def evaluate(self, scope: dict[str, int]) -> int:
                 stack.append(scope[token])
             elif isinstance(token, _DLTypeOperator):  # pyright: ignore[reportUnnecessaryIsInstance]
                 b = stack.pop()
+                if token in _unary_operators:
+                    stack.append(token.evaluate_unary(b))
+                    continue
                 a = stack.pop()
                 stack.append(token.evaluate(a, b))
             else:
@@ -265,19 +280,16 @@ def _maybe_parse_functional_expression(
     # Strip function name and opening parenthesis
     content = expression[len(function.value) + 1 :]
 
-    # Must end with closing parenthesis
-    if not content.endswith(")"):
-        msg = f"Invalid function expression: {expression}, missing closing parenthesis"
-        raise SyntaxError(msg)
-
     # Remove closing parenthesis
     content = content[:-1]
 
     # Find the comma that separates arguments (accounting for nesting)
     depth = 0
-    comma_index = -1
+    balanced_content: list[str] = []
+    current_span = ""
 
-    for i, char in enumerate(content):
+    for char in content:
+        current_span += char
         if char == "(":
             depth += 1
         elif char == ")":
@@ -286,25 +298,23 @@ def _maybe_parse_functional_expression(
                 msg = f"Unbalanced parentheses in function expression: {expression}"
                 raise SyntaxError(msg)
         elif char == "," and depth == 0:
-            comma_index = i
-            break
+            balanced_content.append(current_span[:-1])
+            current_span = ""
+    balanced_content.append(current_span)
 
-    if comma_index == -1:
-        msg = f"Invalid function expression: {expression}, expected two arguments separated by comma"
+    if function in _binary_operators and len(balanced_content) != 2:  # noqa: PLR2004
+        msg = f"Function {function.value} requires 2 arguments, got {len(balanced_content)} in {expression=}"
+        raise SyntaxError(msg)
+    if function in _unary_operators and len(balanced_content) != 1:
+        msg = f"Function {function.value} requires 1 argument, got {len(balanced_content)} in {expression=}"
         raise SyntaxError(msg)
 
-    # Split arguments and parse recursively
-    arg1 = content[:comma_index].strip()
-    arg2 = content[comma_index + 1 :].strip()
-
-    # Recursively parse both arguments
-    expr_1 = expression_from_string(arg1)
-    expr_2 = expression_from_string(arg2)
+    expressions = [expression_from_string(exp) for exp in balanced_content]
 
     # Build postfix expression: [arg1 tokens, arg2 tokens, function]
     return DLTypeDimensionExpression(
         identifier,
-        [*expr_1.parsed_expression, *expr_2.parsed_expression, function],
+        [*list(itertools.chain(*[exp.parsed_expression for exp in expressions])), function],
     )
 
 
diff --git a/dltype/tests/parser_test.py b/dltype/tests/parser_test.py
index e28144a..31d79e7 100644
--- a/dltype/tests/parser_test.py
+++ b/dltype/tests/parser_test.py
@@ -31,6 +31,11 @@
         ("max(3^x,min(3-y,99))", {"x": 2, "y": 4}, 9),
         ("min(3^x,3-y)", {"x": 2, "y": 4}, -1),
         ("variable_name_with_underscores", {"variable_name_with_underscores": 1}, 1),
+        ("isqrt(5)", {}, 2),
+        ("isqrt(16)", {}, 4),
+        ("isqrt(x-y)", {"x": 20, "y": 5}, 3),
+        ("min(isqrt(20),isqrt(16))", {}, 4),
+        ("max(isqrt(20),isqrt(16))", {}, 4),
     ],
 )
 def test_parse_expression(
@@ -52,6 +57,10 @@ def test_parse_expression(
         ("*batch", {}),
         ("3**2", {}),
         ("^", {}),
+        ("isqrt(4, 5)", {}),
+        ("isqrt()", {}),
+        ("max(1)", {}),
+        ("min()", {}),
     ],
 )
 def test_parse_invalid_expression(expression: str, scope: dict[str, int]) -> None: