diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index dafc3b5f..780019e2 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -39,13 +39,13 @@ jobs:
             julia-version: '1.10'
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: "Set up Julia"
-        uses: julia-actions/setup-julia@v1
+        uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.julia-version }}
       - name: "Cache artifacts"
-        uses: julia-actions/cache@v1
+        uses: julia-actions/cache@v2
       - name: "Build package"
         uses: julia-actions/julia-buildpkg@v1
       - name: "Run tests"
@@ -75,11 +75,11 @@ jobs:
           # - "enzyme"  # flaky; seems to infinitely compile and fail the CI
           - "jet"
     steps:
-      - uses: actions/checkout@v2
-      - uses: julia-actions/setup-julia@v1
+      - uses: actions/checkout@v4
+      - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.julia-version }}
-      - uses: julia-actions/cache@v1
+      - uses: julia-actions/cache@v2
       - uses: julia-actions/julia-buildpkg@v1
       - name: Run tests
         id: run-tests
diff --git a/src/Parse.jl b/src/Parse.jl
index d1aac2b6..e6a3805a 100644
--- a/src/Parse.jl
+++ b/src/Parse.jl
@@ -242,6 +242,54 @@ end
     end
 end
 
+@unstable parse_expression(ex::String; kws...) = parse_expression(Meta.parse(ex); kws...)
+
+"""
+Find an operator function by its name in the OperatorEnum, considering the arity.
+Throws appropriate errors for ambiguous or missing matches.
+"""
+@unstable function _find_operator_by_name(func_symbol, degree, operators)
+    matches = Tuple{Function,Int}[]
+
+    for arity in 1:length(operators.ops)
+        for op in operators.ops[arity]
+            if nameof(op) == func_symbol
+                push!(matches, (op, arity))
+            end
+        end
+    end
+
+    if isempty(matches)
+        throw(
+            ArgumentError(
+                "Tried to interpolate function `$(func_symbol)` but failed. " *
+                "Function not found in operators.",
+            ),
+        )
+    end
+
+    arity_matches = filter(m -> m[2] == degree, matches)
+
+    if length(arity_matches) > 1
+        throw(
+            ArgumentError(
+                "Ambiguous operator `$(func_symbol)` with arity $(degree). " *
+                "Multiple matches found: $(arity_matches)",
+            ),
+        )
+    elseif length(arity_matches) == 0
+        available_arities = [m[2] for m in matches]
+        throw(
+            ArgumentError(
+                "Operator `$(func_symbol)` found but not with arity $(degree). " *
+                "Available arities: $(available_arities)",
+            ),
+        )
+    end
+
+    return arity_matches[1][1]::Function
+end
+
 """An empty module for evaluation without collisions."""
 module EmptyModule end
 
@@ -264,9 +312,9 @@ module EmptyModule end
     func = try
         Core.eval(EmptyModule, first(ex.args))
     catch
-        throw(
-            ArgumentError("Tried to interpolate function `$(first(ex.args))` but failed."),
-        )
+        # Try to find the function in operators by name
+        degree = length(args) - 1
+        _find_operator_by_name(first(ex.args), degree, operators)
     end::Function
     return _parse_expression(
         func, args, operators, variable_names, N, E, evaluate_on; kws...
diff --git a/test/test_parse.jl b/test/test_parse.jl
index f801a740..b57d953a 100644
--- a/test/test_parse.jl
+++ b/test/test_parse.jl
@@ -340,3 +340,57 @@ end
     )
     @test string_tree(ex) == "x"
 end
+
+@testitem "custom operators without passing function object" begin
+    using DynamicExpressions
+
+    custom_mul(x, y) = x * y
+    custom_cos(x) = cos(x)
+    custom_max(x, y, z) = max(x, y, z)
+
+    operators = OperatorEnum(
+        1 => [custom_cos], 2 => [+, -, *, /, custom_mul], 3 => [custom_max]
+    )
+
+    # Test nested custom operators
+    ex = parse_expression(
+        "custom_max(custom_cos(x1), custom_mul(x2, x3), x2 + 1.5)";
+        operators=operators,
+        node_type=Node{T,3} where {T},
+        variable_names=["x1", "x2", "x3"],
+    )
+    @test typeof(ex) <: Expression{Float64}
+    @test string_tree(ex) == "custom_max(custom_cos(x1), custom_mul(x2, x3), x2 + 1.5)"
+    @test ex([1.0 2.0 3.0]') == [6.0]
+
+    # Test error cases for _find_operator_by_name
+    @test_throws(
+        ArgumentError(
+            "Tried to interpolate function `unknown_func` but failed. Function not found in operators.",
+        ),
+        parse_expression("unknown_func(x1)", operators=operators, variable_names=["x1"])
+    )
+
+    # Test ambiguous operator - same name from different modules
+    module TestMod1
+    foo(x) = x + 1
+    end
+    module TestMod2
+    foo(x) = x - 1
+    end
+    same_name_ops = OperatorEnum(1 => [TestMod1.foo, TestMod2.foo])
+    @test_throws(
+        r"Ambiguous operator `foo` with arity 1\. Multiple matches found: Tuple\{Function, Int64\}\[.*foo.*1.*foo.*1.*\]",
+        parse_expression("foo(x1)", operators=same_name_ops, variable_names=["x1"])
+    )
+
+    # Test wrong arity
+    @test_throws(
+        ArgumentError(
+            "Operator `custom_cos` found but not with arity 2. Available arities: [1]"
+        ),
+        parse_expression(
+            "custom_cos(x1, x2)", operators=operators, variable_names=["x1", "x2"]
+        )
+    )
+end