diff --git a/idl/Collector.json5 b/idl/Collector.json5
index 6cc8243..19c4490 100644
--- a/idl/Collector.json5
+++ b/idl/Collector.json5
@@ -50,7 +50,7 @@
             noexcept: true,
             attributes: [],
         },
-        // size_type reserved(Generation g, role r) const noexcept
+        // size_type committed(Generation g, role r) const noexcept
         {
             name: "committed",
             doc: ["memory committed for this collector"],
@@ -76,6 +76,22 @@
             noexcept: true,
             attributes: [],
         },
+        // int32_t locate() const noexcept
+        {
+            name: "locate_address",
+            doc: [
+                "Location of object in collector. -1 if not in collector memory.",
+                "Other negative values represent collector error states (good luck!).",
+                "Exact meaning of non-negative values up to collector implementation"
+            ],
+            return_type: "std::int32_t",
+            args: [
+                {type: "const void *", name: "addr"},
+            ],
+            const: true,
+            noexcept: true,
+            attributes: [],
+        },
         // bool contains(role r, const void * addr) const noexcept
         {
             name: "contains",
diff --git a/include/xo/alloc2/gc/ACollector.hpp b/include/xo/alloc2/gc/ACollector.hpp
index 432d382..e682222 100644
--- a/include/xo/alloc2/gc/ACollector.hpp
+++ b/include/xo/alloc2/gc/ACollector.hpp
@@ -65,6 +65,10 @@ public:
     virtual size_type committed(Copaque data, Generation g, role r)  const  noexcept = 0;
     /** address space reserved for this collector **/
     virtual size_type reserved(Copaque data, Generation g, role r)  const  noexcept = 0;
+    /** Location of object in collector. -1 if not in collector memory.
+Other negative values represent collector error states (good luck!).
+Exact meaning of non-negative values up to collector implementation **/
+    virtual std::int32_t locate_address(Copaque data, const void * addr)  const  noexcept = 0;
     /** true if gc responsible for data at @p addr, and data belongs to role @p r **/
     virtual bool contains(Copaque data, role r, const void * addr)  const  noexcept = 0;
     /** true iff gc-aware object of type @p tseq is installed in this collector **/
diff --git a/include/xo/alloc2/gc/ICollector_Any.hpp b/include/xo/alloc2/gc/ICollector_Any.hpp
index d578931..3847243 100644
--- a/include/xo/alloc2/gc/ICollector_Any.hpp
+++ b/include/xo/alloc2/gc/ICollector_Any.hpp
@@ -62,6 +62,7 @@ namespace mm {
         [[noreturn]] size_type allocated(Copaque, Generation, role)  const  noexcept override { _fatal(); }
         [[noreturn]] size_type committed(Copaque, Generation, role)  const  noexcept override { _fatal(); }
         [[noreturn]] size_type reserved(Copaque, Generation, role)  const  noexcept override { _fatal(); }
+        [[noreturn]] std::int32_t locate_address(Copaque, const void *)  const  noexcept override { _fatal(); }
         [[noreturn]] bool contains(Copaque, role, const void *)  const  noexcept override { _fatal(); }
         [[noreturn]] bool is_type_installed(Copaque, typeseq)  const  noexcept override { _fatal(); }
         [[noreturn]] bool report_statistics(Copaque, obj<AAllocator>, obj<AAllocator>, obj<AGCObject> *)  const  noexcept override { _fatal(); }
diff --git a/include/xo/alloc2/gc/ICollector_Xfer.hpp b/include/xo/alloc2/gc/ICollector_Xfer.hpp
index 77cde5f..4293817 100644
--- a/include/xo/alloc2/gc/ICollector_Xfer.hpp
+++ b/include/xo/alloc2/gc/ICollector_Xfer.hpp
@@ -55,6 +55,9 @@ namespace mm {
         size_type reserved(Copaque data, Generation g, role r)  const  noexcept override {
             return I::reserved(_dcast(data), g, r);
         }
+        std::int32_t locate_address(Copaque data, const void * addr)  const  noexcept override {
+            return I::locate_address(_dcast(data), addr);
+        }
         bool contains(Copaque data, role r, const void * addr)  const  noexcept override {
             return I::contains(_dcast(data), r, addr);
         }
diff --git a/include/xo/alloc2/gc/RCollector.hpp b/include/xo/alloc2/gc/RCollector.hpp
index be44e90..47dac46 100644
--- a/include/xo/alloc2/gc/RCollector.hpp
+++ b/include/xo/alloc2/gc/RCollector.hpp
@@ -88,6 +88,9 @@ public:
     size_type reserved(Generation g, role r)  const  noexcept {
         return O::iface()->reserved(O::data(), g, r);
     }
+    std::int32_t locate_address(const void * addr)  const  noexcept {
+        return O::iface()->locate_address(O::data(), addr);
+    }
     bool contains(role r, const void * addr)  const  noexcept {
         return O::iface()->contains(O::data(), r, addr);
     }