diff --git a/hugr-passes/src/dataflow/datalog.rs b/hugr-passes/src/dataflow/datalog.rs
index b814b6440..8dfd98081 100644
--- a/hugr-passes/src/dataflow/datalog.rs
+++ b/hugr-passes/src/dataflow/datalog.rs
@@ -87,7 +87,7 @@ impl<V: AbstractValue> Machine<V> {
                     context
                         .get_optype(*n)
                         .as_func_defn()
-                        .is_some_and(|f| f.name() == "main")
+                        .is_some_and(|f| f.name == "main")
                 });
                 if main.is_none() && in_values.next().is_some() {
                     panic!("Cannot give inputs to module with no 'main'");
diff --git a/hugr-passes/src/dataflow/test.rs b/hugr-passes/src/dataflow/test.rs
index c0fbf395a..dafdb8046 100644
--- a/hugr-passes/src/dataflow/test.rs
+++ b/hugr-passes/src/dataflow/test.rs
@@ -1,6 +1,6 @@
 use ascent::{lattice::BoundedLattice, Lattice};
 
-use hugr_core::builder::{CFGBuilder, Container, DataflowHugr};
+use hugr_core::builder::{CFGBuilder, Container, DataflowHugr, ModuleBuilder};
 use hugr_core::hugr::views::{DescendantsGraph, HierarchyView};
 use hugr_core::ops::handle::DfgID;
 use hugr_core::ops::TailLoop;
@@ -483,3 +483,70 @@ fn test_region() {
         );
     }
 }
+
+#[test]
+fn test_module() {
+    let mut modb = ModuleBuilder::new();
+    let leaf_fn = modb
+        .define_function("leaf", Signature::new_endo(type_row![BOOL_T; 2]))
+        .unwrap();
+    let outs = leaf_fn.input_wires();
+    let leaf_fn = leaf_fn.finish_with_outputs(outs).unwrap();
+
+    let mut f2 = modb
+        .define_function("f2", Signature::new(BOOL_T, type_row![BOOL_T; 2]))
+        .unwrap();
+    let [inp] = f2.input_wires_arr();
+    let cst_true = f2.add_load_value(Value::true_val());
+    let f2_call = f2
+        .call(&leaf_fn.handle(), &[], [inp, cst_true], &EMPTY_REG)
+        .unwrap();
+    let f2 = f2.finish_with_outputs(f2_call.outputs()).unwrap();
+
+    let mut main = modb
+        .define_function("main", Signature::new(BOOL_T, type_row![BOOL_T; 2]))
+        .unwrap();
+    let [inp] = main.input_wires_arr();
+    let cst_false = main.add_load_value(Value::false_val());
+    let main_call = main
+        .call(&leaf_fn.handle(), &[], [inp, cst_false], &EMPTY_REG)
+        .unwrap();
+    main.finish_with_outputs(main_call.outputs()).unwrap();
+    let hugr = modb.finish_hugr(&EMPTY_REG).unwrap();
+    let [f2_inp, _] = hugr.get_io(f2.node()).unwrap();
+
+    let results_just_main = Machine::default().run(TestContext(&hugr), [(0.into(), pv_true())]);
+    assert_eq!(
+        results_just_main.read_out_wire(Wire::new(f2_inp, 0)),
+        Some(PartialValue::Bottom)
+    );
+    for call in [f2_call, main_call] {
+        // The first output of the Call comes from `main` because no value was fed in from f2
+        assert_eq!(
+            results_just_main.read_out_wire(Wire::new(call.node(), 0)),
+            Some(pv_true().into())
+        );
+        // (Without reachability) the second output of the Call is the join of the two constant inputs from the two calls
+        assert_eq!(
+            results_just_main.read_out_wire(Wire::new(call.node(), 1)),
+            Some(pv_true_or_false().into())
+        );
+    }
+
+    let results_two_calls = {
+        let mut m = Machine::default();
+        m.prepopulate_df_inputs(&hugr, f2.node(), [(0.into(), pv_true())]);
+        m.run(TestContext(&hugr), [(0.into(), pv_false())])
+    };
+
+    for call in [f2_call, main_call] {
+        assert_eq!(
+            results_two_calls.read_out_wire(Wire::new(call.node(), 0)),
+            Some(pv_true_or_false().into())
+        );
+        assert_eq!(
+            results_two_calls.read_out_wire(Wire::new(call.node(), 1)),
+            Some(pv_true_or_false().into())
+        );
+    }
+}