diff --git a/src/script_opt/GenIDDefs.cc b/src/script_opt/GenIDDefs.cc
index ef7ca32704..6eaf77576d 100644
--- a/src/script_opt/GenIDDefs.cc
+++ b/src/script_opt/GenIDDefs.cc
@@ -107,37 +107,8 @@ TraversalCode GenIDDefs::PreStmt(const Stmt* s)
 			}
 
 		case STMT_SWITCH:
-			{
-			auto sw = s->AsSwitchStmt();
-			auto e = sw->StmtExpr();
-
-			e->Traverse(this);
-
-			StartConfluenceBlock(sw);
-
-			for ( const auto& c : *sw->Cases() )
-				{
-				auto body = c->Body();
-
-				auto exprs = c->ExprCases();
-				if ( exprs )
-					exprs->Traverse(this);
-
-				auto type_ids = c->TypeCases();
-				if ( type_ids )
-					{
-					for ( const auto& id : *type_ids )
-						if ( id->Name() )
-							TrackID(id);
-					}
-
-				body->Traverse(this);
-				}
-
-			EndConfluenceBlock(sw->HasDefault());
-
+			AnalyzeSwitch(s->AsSwitchStmt());
 			return TC_ABORTSTMT;
-			}
 
 		case STMT_FOR:
 			{
@@ -201,6 +172,38 @@ TraversalCode GenIDDefs::PreStmt(const Stmt* s)
 		}
 	}
 
+void GenIDDefs::AnalyzeSwitch(const SwitchStmt* sw)
+	{
+	sw->StmtExpr()->Traverse(this);
+
+	for ( const auto& c : *sw->Cases() )
+		{
+		// Important: the confluence block is the switch statement
+		// itself, not the case body.  This is needed so that variable
+		// assignments made inside case bodies that end with
+		// "fallthrough" are correctly propagated to the next case
+		// body.
+		StartConfluenceBlock(sw);
+
+		auto body = c->Body();
+
+		auto exprs = c->ExprCases();
+		if ( exprs )
+			exprs->Traverse(this);
+
+		auto type_ids = c->TypeCases();
+		if ( type_ids )
+			{
+			for ( const auto& id : *type_ids )
+				if ( id->Name() )
+					TrackID(id);
+			}
+
+		body->Traverse(this);
+		EndConfluenceBlock(false);
+		}
+	}
+
 TraversalCode GenIDDefs::PostStmt(const Stmt* s)
 	{
 	switch ( s->Tag() )
diff --git a/src/script_opt/GenIDDefs.h b/src/script_opt/GenIDDefs.h
index 29593e458c..8667394b14 100644
--- a/src/script_opt/GenIDDefs.h
+++ b/src/script_opt/GenIDDefs.h
@@ -22,6 +22,8 @@ private:
 	void TraverseFunction(const Func* f, ScopePtr scope, StmtPtr body);
 
 	TraversalCode PreStmt(const Stmt*) override;
+	void AnalyzeSwitch(const SwitchStmt* sw);
+
 	TraversalCode PostStmt(const Stmt*) override;
 	TraversalCode PreExpr(const Expr*) override;
 	TraversalCode PostExpr(const Expr*) override;
diff --git a/src/script_opt/Stmt.cc b/src/script_opt/Stmt.cc
index 7da1343361..7cefdc63a2 100644
--- a/src/script_opt/Stmt.cc
+++ b/src/script_opt/Stmt.cc
@@ -320,13 +320,20 @@ IntrusivePtr<Case> Case::Duplicate()
 		return make_intrusive<Case>(new_exprs, nullptr, s->Duplicate());
 		}
 
+	IDPList* new_type_cases = nullptr;
+
 	if ( type_cases )
 		{
+		new_type_cases = new IDPList();
+
 		for ( auto tc : *type_cases )
+			{
 			zeek::Ref(tc);
+			new_type_cases->append(tc);
+			}
 		}
 
-	return make_intrusive<Case>(nullptr, type_cases, s->Duplicate());
+	return make_intrusive<Case>(nullptr, new_type_cases, s->Duplicate());
 	}
 
 StmtPtr SwitchStmt::Duplicate()
@@ -354,6 +361,9 @@ bool SwitchStmt::IsReduced(Reducer* r) const
 	if ( ! e->IsReduced(r) )
 		return NonReduced(e.get());
 
+	if ( cases->length() == 0 )
+		return false;
+
 	for ( const auto& c : *cases )
 		{
 		if ( c->ExprCases() && ! c->ExprCases()->IsReduced(r) )
@@ -371,6 +381,10 @@ bool SwitchStmt::IsReduced(Reducer* r) const
 
 StmtPtr SwitchStmt::DoReduce(Reducer* rc)
 	{
+	if ( cases->length() == 0 )
+		// Degenerate.
+		return make_intrusive<NullStmt>();
+
 	auto s = make_intrusive<StmtList>();
 	StmtPtr red_e_stmt;
 
@@ -388,7 +402,8 @@ StmtPtr SwitchStmt::DoReduce(Reducer* rc)
 	for ( auto& i : case_label_type_list )
 		{
 		IDPtr idp = {NewRef{}, i.first};
-		i.first = rc->UpdateID(idp).release();
+		if ( idp->Name() )
+			i.first = rc->UpdateID(idp).release();
 		}
 
 	for ( const auto& c : *cases )
@@ -405,7 +420,11 @@ StmtPtr SwitchStmt::DoReduce(Reducer* rc)
 
 		auto c_t = c->TypeCases();
 		if ( c_t )
-			rc->UpdateIDs(c_t);
+			{
+			for ( auto& c_t_i : *c_t )
+				if ( c_t_i->Name() )
+					c_t_i = rc->UpdateID({NewRef{}, c_t_i}).release();
+			}
 
 		c->UpdateBody(c->Body()->Reduce(rc));
 		}