diff --git a/LiteCore/Logging/Logging.cc b/LiteCore/Logging/Logging.cc
index 4950ac0f0..25fc2b8b6 100644
--- a/LiteCore/Logging/Logging.cc
+++ b/LiteCore/Logging/Logging.cc
@@ -117,9 +117,7 @@ namespace litecore {
                           .fileOnly  = !doCallback};
         if ( logger ) {
             entry.objRef = logger->getObjectRef();
-            std::stringstream prefixOut;
-            logger->addLoggingKeyValuePairs(prefixOut);
-            prefix = prefixOut.str();
+            prefix       = logger->loggingKeyValuePairs();
         }
 
         unique_lock<mutex> lock(sLogMutex);
diff --git a/LiteCore/Logging/Logging.hh b/LiteCore/Logging/Logging.hh
index 974ec9c3e..22fc83049 100644
--- a/LiteCore/Logging/Logging.hh
+++ b/LiteCore/Logging/Logging.hh
@@ -16,7 +16,6 @@
 #include <cstdarg>
 #include <cstdint>
 #include <cinttypes>  //for stdint.h fmt specifiers
-#include <iosfwd>
 #include <string>
 
 /*
@@ -153,6 +152,11 @@ namespace litecore {
         virtual std::string loggingIdentifier() const;
         virtual std::string loggingClassName() const;
 
+        /** Override this to return aditional metadata about the object, in the form of
+            space-separated "key=value" pairs.
+            These will be logged with every message, even in the binary log file. */
+        virtual std::string loggingKeyValuePairs() const { return {}; }
+
 #define LOGBODY_(LEVEL)                                                                                                \
     va_list args;                                                                                                      \
     va_start(args, format);                                                                                            \
@@ -177,11 +181,6 @@ namespace litecore {
 
         void _logv(LogLevel level, const char* format, va_list) const __printflike(3, 0);
 
-        /// Add key=value pairs to the output. They are space separated. If output is not empty
-        /// upon entry, add a space to start new key=value pairs.
-        /// Warning: the string must not include printf format specifier, '%'.
-        virtual void addLoggingKeyValuePairs(std::stringstream& output) const {}
-
         LogDomain& _domain;
 
       private:
diff --git a/LiteCore/tests/LogObserverTest.hh b/LiteCore/tests/LogObserverTest.hh
index 1af4ee227..dedd48aac 100644
--- a/LiteCore/tests/LogObserverTest.hh
+++ b/LiteCore/tests/LogObserverTest.hh
@@ -14,7 +14,6 @@
 #include "Logging.hh"
 #include "LogObserver.hh"
 #include <queue>
-#include <sstream>
 
 using namespace std;
 using namespace litecore;
@@ -32,7 +31,7 @@ class LogObject : public Logging {
 
     std::string loggingClassName() const override { return _identifier; }
 
-    void addLoggingKeyValuePairs(std::stringstream& output) const override { output << _kv; }
+    std::string loggingKeyValuePairs() const override { return _kv; }
 
     LogObjectRef getRef() const { return getObjectRef(); }
 
diff --git a/Replicator/Replicator.cc b/Replicator/Replicator.cc
index e985223ad..8f1878971 100644
--- a/Replicator/Replicator.cc
+++ b/Replicator/Replicator.cc
@@ -1353,12 +1353,14 @@ namespace litecore::repl {
         }
     }
 
-    void Replicator::addLoggingKeyValuePairs(std::stringstream& output) const {
-        Worker::addLoggingKeyValuePairs(output);
+    string Replicator::loggingKeyValuePairs() const {
+        string kv = Worker::loggingKeyValuePairs();
         if ( _correlationID ) {
-            if ( output.tellp() > 0 ) output << " ";
-            output << "CorrID=" << _correlationID.asString();
+            if ( !kv.empty() ) kv += " ";
+            kv += "CorrID=";
+            kv += _correlationID.asString();
         }
+        return kv;
     }
 
 }  // namespace litecore::repl
diff --git a/Replicator/Replicator.hh b/Replicator/Replicator.hh
index 06ecc2e11..b74c11003 100644
--- a/Replicator/Replicator.hh
+++ b/Replicator/Replicator.hh
@@ -117,7 +117,7 @@ namespace litecore::repl {
       protected:
         std::string loggingClassName() const override { return _options->isActive() ? "Repl" : "PsvRepl"; }
 
-        void addLoggingKeyValuePairs(std::stringstream& output) const override;
+        std::string loggingKeyValuePairs() const override;
 
         // BLIP ConnectionDelegate API:
         void onHTTPResponse(int status, const websocket::Headers& headers) override;
diff --git a/Replicator/Worker.cc b/Replicator/Worker.cc
index ece17bf0a..aad81d299 100644
--- a/Replicator/Worker.cc
+++ b/Replicator/Worker.cc
@@ -328,12 +328,14 @@ namespace litecore::repl {
         return nonConstThis->replicator()->collection(collectionIndex());
     }
 
-    void Worker::addLoggingKeyValuePairs(std::stringstream& output) const {
-        actor::Actor::addLoggingKeyValuePairs(output);
+    string Worker::loggingKeyValuePairs() const {
+        string kv = Actor::loggingKeyValuePairs();
         if ( auto collIdx = collectionIndex(); collIdx != kNotCollectionIndex ) {
-            if ( output.tellp() > 0 ) output << " ";
-            output << "Coll=" << collIdx;
+            if ( !kv.empty() ) kv += " ";
+            kv += "Coll=";
+            kv += to_string(collIdx);
         }
+        return kv;
     }
 
     const std::unordered_set<slice> Options::kWhiteListOfKeysToLog{
diff --git a/Replicator/Worker.hh b/Replicator/Worker.hh
index e03812f59..4e692582c 100644
--- a/Replicator/Worker.hh
+++ b/Replicator/Worker.hh
@@ -241,7 +241,7 @@ namespace litecore::repl {
 
         const C4Collection* getCollection() const;
 
-        void addLoggingKeyValuePairs(std::stringstream& output) const override;
+        std::string loggingKeyValuePairs() const override;
 
         RetainedConst<Options>    _options;        // The replicator options
         Retained<Worker>          _parent;         // Worker that owns me