diff --git a/hugr-py/src/hugr/build/dfg.py b/hugr-py/src/hugr/build/dfg.py
index 8af4ae1ad..48a710df7 100644
--- a/hugr-py/src/hugr/build/dfg.py
+++ b/hugr-py/src/hugr/build/dfg.py
@@ -510,7 +510,10 @@ def add_state_order(self, src: Node, dst: Node) -> None:
             [Node(2)]
         """
         # adds edge to the right of all existing edges
-        self.hugr.add_link(src.out(-1), dst.inp(-1))
+        source = src.out(-1)
+        target = dst.inp(-1)
+        if not self.hugr.has_link(source, target):
+            self.hugr.add_link(source, target)
 
     def load(
         self, const: ToNode | val.Value, const_parent: ToNode | None = None
@@ -616,6 +619,12 @@ def _wire_up(self, node: Node, ports: Iterable[Wire]) -> tys.TypeRow:
         tys = [self._wire_up_port(node, i, p) for i, p in enumerate(ports)]
         if isinstance(op := self.hugr[node].op, ops._PartialOp):
             op._set_in_types(tys)
+            if isinstance(op, ops.DataflowOp):
+                # Update the node's input and output port count
+                sig = op.outer_signature()
+                self.hugr._update_port_count(
+                    node, num_inps=len(sig.input), num_outs=len(sig.output)
+                )
         return tys
 
     def _get_dataflow_type(self, wire: Wire) -> tys.Type:
diff --git a/hugr-py/src/hugr/hugr/base.py b/hugr-py/src/hugr/hugr/base.py
index 979021057..14e40e795 100644
--- a/hugr-py/src/hugr/hugr/base.py
+++ b/hugr-py/src/hugr/hugr/base.py
@@ -182,12 +182,31 @@ def _update_node_outs(self, node: Node, num_outs: int | None) -> Node:
         Returns:
             The updated node.
         """
-        self[node]._num_outs = num_outs or 0
-        node = replace(node, _num_out_ports=num_outs)
-        parent = self[node].parent
-        if parent is not None:
-            pos = self[parent].children.index(node)
-            self[parent].children[pos] = node
+        return self._update_port_count(node, num_outs=num_outs)
+
+    def _update_port_count(
+        self, node: Node, *, num_inps: int | None = None, num_outs: int | None
+    ) -> Node:
+        """Update the number of incoming and outgoing ports for a node.
+
+        If `num_inps` or `num_outs` is None, the corresponding count is not updated.
+
+        Returns:
+            The updated node.
+        """
+        if num_inps is None and num_outs is None:
+            return node
+
+        if num_inps is not None:
+            self[node]._num_inps = num_inps
+        if num_outs is not None:
+            self[node]._num_outs = num_outs
+            node = replace(node, _num_out_ports=num_outs)
+            parent = self[node].parent
+            if parent is not None:
+                pos = self[parent].children.index(node)
+                self[parent].children[pos] = node
+
         return node
 
     def add_node(
@@ -284,6 +303,24 @@ def _unused_sub_offset(self, port: P) -> _SubPort[P]:
             sub_port = sub_port.next_sub_offset()
         return sub_port
 
+    def has_link(self, src: OutPort, dst: InPort) -> bool:
+        """Check if there is a link between two ports.
+
+        Args:
+            src: Source port.
+            dst: Destination port.
+
+        Returns:
+            True if there is a link, False otherwise.
+
+        Examples:
+            >>> df = dfg.Dfg(tys.Bool)
+            >>> df.hugr.add_link(df.input_node.out(0), df.output_node.inp(0))
+            >>> df.hugr.has_link(df.input_node.out(0), df.output_node.inp(0))
+            True
+        """
+        return dst in self.linked_ports(src)
+
     def add_link(self, src: OutPort, dst: InPort) -> None:
         """Add a link (edge) between two nodes to the HUGR,
           from an outgoing port to an incoming port.
@@ -604,14 +641,11 @@ def _serialize_link(
         )
 
     def _constrain_offset(self, p: P) -> PortOffset:
-        # negative offsets are used to refer to the last port
+        # An offset of -1 is a special case, indicating an order edge,
+        # not counted in the number of ports.
         if p.offset < 0:
-            match p.direction:
-                case Direction.INCOMING:
-                    current = self.num_incoming(p.node)
-                case Direction.OUTGOING:
-                    current = self.num_outgoing(p.node)
-            offset = current + p.offset + 1
+            assert p.offset == -1, "Only order edges are allowed with offset < 0"
+            offset = self.num_ports(p.node, p.direction)
         else:
             offset = p.offset
 
diff --git a/hugr-py/src/hugr/ops.py b/hugr-py/src/hugr/ops.py
index a97470adf..8c5b845a8 100644
--- a/hugr-py/src/hugr/ops.py
+++ b/hugr-py/src/hugr/ops.py
@@ -72,6 +72,11 @@ def name(self) -> str:
 
 
 def _sig_port_type(sig: tys.FunctionType, port: InPort | OutPort) -> tys.Type:
+    """Get the type of the given dataflow port given the signature of the operation."""
+    if port.offset == -1:
+        # Order port
+        msg = "Order port has no type."
+        raise ValueError(msg)
     if port.direction == Direction.INCOMING:
         return sig.input[port.offset]
     return sig.output[port.offset]
diff --git a/hugr-py/tests/test_hugr_build.py b/hugr-py/tests/test_hugr_build.py
index 3f7145a87..2607a4773 100644
--- a/hugr-py/tests/test_hugr_build.py
+++ b/hugr-py/tests/test_hugr_build.py
@@ -316,3 +316,17 @@ def test_alias() -> None:
     _dcl = mod.add_alias_decl("my_bool", tys.TypeBound.Copyable)
 
     validate(mod.hugr)
+
+
+# https://github.com/CQCL/hugr/issues/1625
+def test_dfg_unpack() -> None:
+    dfg = Dfg(tys.Tuple(tys.Bool, tys.Bool))
+    bool1, _unused_bool2 = dfg.add_op(ops.UnpackTuple(), *dfg.inputs())
+    cond = dfg.add_conditional(bool1)
+    with cond.add_case(0) as case:
+        case.set_outputs(bool1)
+    with cond.add_case(1) as case:
+        case.set_outputs(bool1)
+    dfg.set_outputs(*cond.outputs())
+
+    validate(dfg.hugr)