diff --git a/src/Func.cc b/src/Func.cc
index 75d604a560..b0d1889282 100644
--- a/src/Func.cc
+++ b/src/Func.cc
@@ -564,7 +564,7 @@ void ScriptFunc::AddBody(StmtPtr new_body, const std::vector<IDPtr>& new_inits,
 
     Body b;
     b.stmts = new_body;
-    b.groups = groups;
+    b.groups = {groups.begin(), groups.end()};
     current_body = new_body;
     current_priority = b.priority = priority;
 
diff --git a/src/Func.h b/src/Func.h
index 37e1538fa2..4476935d2a 100644
--- a/src/Func.h
+++ b/src/Func.h
@@ -2,6 +2,7 @@
 
 #pragma once
 
+#include <forward_list>
 #include <memory>
 #include <string>
 #include <tuple>
@@ -66,8 +67,8 @@ public:
 
     struct Body {
         detail::StmtPtr stmts;
+        std::forward_list<EventGroupPtr> groups;
         int priority;
-        std::set<EventGroupPtr> groups;
         // If any of the groups are disabled, this body is disabled.
         // The disabled field is updated from EventGroup instances.
         bool disabled = false;