diff --git a/src/libslic3r/SLA/SupportTreeBuilder.hpp b/src/libslic3r/SLA/SupportTreeBuilder.hpp
index 2b3ff91a06..aa8a4ea83b 100644
--- a/src/libslic3r/SLA/SupportTreeBuilder.hpp
+++ b/src/libslic3r/SLA/SupportTreeBuilder.hpp
@@ -58,12 +58,17 @@ template<class Vec> double distance(const Vec& pp1, const Vec& pp2) {
     return distance(p);
 }
 
-const constexpr long ID_UNSET = -1;
-
 const Vec3d DOWN = {0.0, 0.0, -1.0};
 
+struct SupportTreeNode
+{
+    static const constexpr long ID_UNSET = -1;
+
+    long id = ID_UNSET; // For identification withing a tree.
+};
+
 // A pinhead originating from a support point
-struct Head {
+struct Head: public SupportTreeNode {
     Vec3d dir = DOWN;
     Vec3d pos = {0, 0, 0};
     
@@ -71,10 +76,7 @@ struct Head {
     double r_pin_mm = 0.5;
     double width_mm = 2;
     double penetration_mm = 0.5;
-    
-    // For identification purposes. This will be used as the index into the
-    // container holding the head structures. See SLASupportTree::Impl
-    long id = ID_UNSET;
+
     
     // If there is a pillar connecting to this head, then the id will be set.
     long pillar_id = ID_UNSET;
@@ -115,21 +117,17 @@ struct Head {
 };
 
 // A junction connecting bridges and pillars
-struct Junction {
+struct Junction: public SupportTreeNode {
     double r = 1;
     Vec3d pos;
-    
-    long id = ID_UNSET;
 
     Junction(const Vec3d &tr, double r_mm) : r(r_mm), pos(tr) {}
 };
 
-struct Pillar {
+struct Pillar: public SupportTreeNode {
     double height, r;
     Vec3d endpt;
     
-    long id = ID_UNSET;
-    
     // If the pillar connects to a head, this is the id of that head
     bool starts_from_head = true; // Could start from a junction as well
     long start_junction_id = ID_UNSET;
@@ -152,10 +150,9 @@ struct Pillar {
 };
 
 // A base for pillars or bridges that end on the ground
-struct Pedestal {
+struct Pedestal: public SupportTreeNode {
     Vec3d pos;
     double height, r_bottom, r_top;
-    long id = ID_UNSET;
 
     Pedestal(const Vec3d &p, double h, double rbottom, double rtop)
         : pos{p}, height{h}, r_bottom{rbottom}, r_top{rtop}
@@ -167,9 +164,8 @@ struct Pedestal {
 struct Anchor: public Head { using Head::Head; };
 
 // A Bridge between two pillars (with junction endpoints)
-struct Bridge {
+struct Bridge: public SupportTreeNode {
     double r = 0.8;
-    long id = ID_UNSET;
     Vec3d startp = Vec3d::Zero(), endp = Vec3d::Zero();
     
     Bridge(const Vec3d &j1,
diff --git a/src/libslic3r/SLA/SupportTreeBuildsteps.cpp b/src/libslic3r/SLA/SupportTreeBuildsteps.cpp
index c6b2884d26..00f09b8121 100644
--- a/src/libslic3r/SLA/SupportTreeBuildsteps.cpp
+++ b/src/libslic3r/SLA/SupportTreeBuildsteps.cpp
@@ -570,7 +570,7 @@ bool SupportTreeBuildsteps::create_ground_pillar(const Vec3d &jp,
                                                  long         head_id)
 {
     double sd           = m_cfg.pillar_base_safety_distance_mm;
-    long   pillar_id    = ID_UNSET;
+    long   pillar_id    = SupportTreeNode::ID_UNSET;
     bool   can_add_base = radius >= m_cfg.head_back_radius_mm;
     double base_r       = can_add_base ? m_cfg.base_radius_mm : 0.;
     double gndlvl       = m_builder.ground_level;
@@ -1029,7 +1029,7 @@ bool SupportTreeBuildsteps::connect_to_ground(Head &head)
 
 bool SupportTreeBuildsteps::connect_to_model_body(Head &head)
 {
-    if (head.id <= ID_UNSET) return false;
+    if (head.id <= SupportTreeNode::ID_UNSET) return false;
     
     auto it = m_head_to_ground_scans.find(unsigned(head.id));
     if (it == m_head_to_ground_scans.end()) return false;
@@ -1084,7 +1084,7 @@ bool SupportTreeBuildsteps::search_pillar_and_connect(const Head &source)
     // We also need to remove elements progressively from the copied index.
     PointIndex spindex = m_pillar_index.guarded_clone();
 
-    long nearest_id = ID_UNSET;
+    long nearest_id = SupportTreeNode::ID_UNSET;
 
     Vec3d querypt = source.junction_point();
 
@@ -1105,7 +1105,7 @@ bool SupportTreeBuildsteps::search_pillar_and_connect(const Head &source)
             if (size_t(nearest_id) < m_builder.pillarcount()) {
                 if(!connect_to_nearpillar(source, nearest_id) ||
                     m_builder.pillar(nearest_id).r < source.r_back_mm) {
-                    nearest_id = ID_UNSET;    // continue searching
+                    nearest_id = SupportTreeNode::ID_UNSET;    // continue searching
                     spindex.remove(ne);       // without the current pillar
                 }
             }
diff --git a/src/libslic3r/SLA/SupportTreeBuildsteps.hpp b/src/libslic3r/SLA/SupportTreeBuildsteps.hpp
index 51d8344480..e8f73149e3 100644
--- a/src/libslic3r/SLA/SupportTreeBuildsteps.hpp
+++ b/src/libslic3r/SLA/SupportTreeBuildsteps.hpp
@@ -293,7 +293,7 @@ class SupportTreeBuildsteps {
     bool create_ground_pillar(const Vec3d &jp,
                               const Vec3d &sourcedir,
                               double       radius,
-                              long         head_id = ID_UNSET);
+                              long         head_id = SupportTreeNode::ID_UNSET);
 
     void add_pillar_base(long pid)
     {
diff --git a/tests/sla_print/sla_test_utils.cpp b/tests/sla_print/sla_test_utils.cpp
index 4cd94b7ed3..bc0cfb0cd1 100644
--- a/tests/sla_print/sla_test_utils.cpp
+++ b/tests/sla_print/sla_test_utils.cpp
@@ -175,8 +175,8 @@ void check_support_tree_integrity(const sla::SupportTreeBuilder &stree,
     double H2   = cfg.max_dual_pillar_height_mm;
     
     for (const sla::Head &head : stree.heads()) {
-        REQUIRE((!head.is_valid() || head.pillar_id != sla::ID_UNSET ||
-                head.bridge_id != sla::ID_UNSET));
+        REQUIRE((!head.is_valid() || head.pillar_id != sla::SupportTreeNode::ID_UNSET ||
+                head.bridge_id != sla::SupportTreeNode::ID_UNSET));
     }
     
     for (const sla::Pillar &pillar : stree.pillars()) {