diff --git a/src/script_opt/ReachingDefs.cc b/src/script_opt/ReachingDefs.cc
index 197f0327a2..fc243b8486 100644
--- a/src/script_opt/ReachingDefs.cc
+++ b/src/script_opt/ReachingDefs.cc
@@ -9,13 +9,13 @@ namespace zeek::detail {
 
 ReachingDefs::ReachingDefs()
 	{
-	my_rd_map = std::make_unique<ReachingDefsMap>();
+	my_rd_map = std::make_shared<ReachingDefsMap>();
 	const_rd_map = nullptr;
 	}
 
 ReachingDefs::ReachingDefs(RDPtr rd)
 	{
-	const_rd_map = std::move(rd);
+	const_rd_map = rd->RDMap();
 	my_rd_map = nullptr;
 	}
 
@@ -65,7 +65,7 @@ RDPtr ReachingDefs::Intersect(const RDPtr& r) const
 
 	auto res = make_intrusive<ReachingDefs>();
 
-	for ( const auto& i : *RDMap() )
+	for ( const auto& i : *RDMapRef() )
 		for ( const auto& dp : *i.second )
 			{
 			if ( r->HasPair(i.first, dp) )
@@ -87,7 +87,7 @@ RDPtr ReachingDefs::Union(const RDPtr& r) const
 
 	res->AddRDs(r);
 
-	for ( const auto& i : *RDMap() )
+	for ( const auto& i : *RDMapRef() )
 		for ( const auto& dp : *i.second )
 			res->AddRD(i.first, dp);
 
@@ -102,7 +102,7 @@ RDPtr ReachingDefs::IntersectWithConsolidation(const RDPtr& r,
 
 	auto res = make_intrusive<ReachingDefs>();
 
-	for ( const auto& i : *RDMap() )
+	for ( const auto& i : *RDMapRef() )
 		for ( const auto& dp : *i.second )
 			{
 			if ( r->HasPair(i.first, dp) )
@@ -122,7 +122,7 @@ RDPtr ReachingDefs::IntersectWithConsolidation(const RDPtr& r,
 bool ReachingDefs::HasPair(const DefinitionItem* di, const DefinitionPoint& dp)
 const
 	{
-	auto map = RDMap();
+	const auto& map = RDMapRef();
 
 	auto l = map->find(di);
 	if ( l == map->end() )
@@ -135,7 +135,7 @@ const
 	return false;
 	}
 
-void ReachingDefs::AddRDs(const ReachingDefsMap* rd_m)
+void ReachingDefs::AddRDs(const std::shared_ptr<ReachingDefsMap>& rd_m)
 	{
 	for ( const auto& one_rd : *rd_m )
 		for ( const auto& dp : *one_rd.second )
@@ -147,18 +147,18 @@ void ReachingDefs::CopyMapIfNeeded()
 	if ( my_rd_map )
 		return;
 
-	my_rd_map = std::make_unique<ReachingDefsMap>();
-	auto old_const_rd_map = const_rd_map;
+	my_rd_map = std::make_shared<ReachingDefsMap>();
+	auto old_const_rd_map = std::move(const_rd_map);
 	const_rd_map = nullptr;
 	AddRDs(old_const_rd_map);
 	}
 
 void ReachingDefs::Dump() const
 	{
-	DumpMap(RDMap());
+	DumpMap(RDMapRef());
 	}
 
-void ReachingDefs::DumpMap(const ReachingDefsMap* map) const
+void ReachingDefs::DumpMap(const std::shared_ptr<ReachingDefsMap>& map) const
 	{
 	printf("%d RD element%s: ", Size(), Size() == 1 ? "" : "s");
 
diff --git a/src/script_opt/ReachingDefs.h b/src/script_opt/ReachingDefs.h
index fed6657ec7..11605b3bb0 100644
--- a/src/script_opt/ReachingDefs.h
+++ b/src/script_opt/ReachingDefs.h
@@ -45,7 +45,7 @@ public:
 
 	// Add in all the definition points from rd into our set, if
 	// we don't already have them.
-	void AddRDs(const RDPtr& rd)	{ AddRDs(rd->RDMap()); }
+	void AddRDs(const RDPtr& rd)	{ AddRDs(rd->RDMapRef()); }
 
 	// Add in a single definition pair, creating the entry for
 	// the item if necessary.
@@ -59,7 +59,7 @@ public:
 	// True if the given definition item is present in our RDs.
 	bool HasDI(const DefinitionItem* di) const
 		{
-		auto map = RDMap();
+		const auto& map = RDMapRef();
 		return map->find(di) != map->end();
 		}
 
@@ -67,7 +67,7 @@ public:
 	// points at our location in the AST.
 	DefPoints* GetDefPoints(const DefinitionItem* di)
 		{
-		auto map = RDMap();
+		const auto& map = RDMapRef();
 		auto dps = map->find(di);
 		return dps == map->end() ? nullptr : dps->second.get();
 		}
@@ -115,11 +115,11 @@ public:
 	RDPtr IntersectWithConsolidation(const RDPtr& r,
 					const DefinitionPoint& di) const;
 
-	int Size() const	{ return RDMap()->size(); }
+	int Size() const	{ return RDMapRef()->size(); }
 
 	// Print out the RDs, for debugging purposes.
 	void Dump() const;
-	void DumpMap(const ReachingDefsMap* map) const;
+	void DumpMap(const std::shared_ptr<ReachingDefsMap>& map) const;
 
 protected:
 	// True if our RDs include the given definition item, defined at
@@ -127,10 +127,13 @@ protected:
 	bool HasPair(const DefinitionItem* di, const DefinitionPoint& dp) const;
 
 	// Adds in the given RDs if we don't already have them.
-	void AddRDs(const ReachingDefsMap* rd_m);
+	void AddRDs(const std::shared_ptr<ReachingDefsMap>& rd_m);
 
-	const ReachingDefsMap* RDMap() const
-		{ return my_rd_map ? my_rd_map.get() : const_rd_map->RDMap(); }
+	std::shared_ptr<ReachingDefsMap> RDMap() const
+		{ return my_rd_map ? my_rd_map : const_rd_map; }
+
+	const std::shared_ptr<ReachingDefsMap>& RDMapRef() const
+		{ return my_rd_map ? my_rd_map : const_rd_map; }
 
 	// If we don't already have our own map, copy the one we're using
 	// so that we then do.
@@ -140,9 +143,11 @@ protected:
 	void PrintRD(const DefinitionItem* di, const DefinitionPoint& dp) const;
 
 	// If my_rd_map is non-nil, then we use that map.  Otherwise,
-	// we use the map that const_rd_map points to.
-	RDPtr const_rd_map;
-	std::unique_ptr<ReachingDefsMap> my_rd_map;
+	// we use the map that const_rd_map points to.  The "const" in
+	// the latter's name is a reminder to not make any changes to
+	// that map.
+	std::shared_ptr<ReachingDefsMap> my_rd_map;
+	std::shared_ptr<ReachingDefsMap> const_rd_map;
 };