diff --git a/app/models/issue_query.rb b/app/models/issue_query.rb
index 3431750f6..ecd925716 100644
--- a/app/models/issue_query.rb
+++ b/app/models/issue_query.rb
@@ -589,9 +589,7 @@ class IssueQuery < Query
     end
     groups ||= []
 
-    members_of_groups = groups.inject([]) do |user_ids, group|
-      user_ids + group.user_ids + [group.id]
-    end.uniq.compact.sort.collect(&:to_s)
+    members_of_groups = group_and_member_ids(groups)
 
     '(' + sql_for_field("assigned_to_id", operator, members_of_groups, Issue.table_name, "assigned_to_id", false) + ')'
   end
@@ -627,13 +625,27 @@ class IssueQuery < Query
   def sql_for_author_group_field(field, operator, value)
     groups = value.empty? ? Group.givable : Group.where(:id => value).to_a
 
-    author_groups = groups.inject([]) do |user_ids, group|
-      user_ids + group.user_ids + [group.id]
-    end.uniq.compact.sort.collect(&:to_s)
+    author_groups = group_and_member_ids(groups)
 
     '(' + sql_for_field("author_id", operator, author_groups, Issue.table_name, "author_id", false) + ')'
   end
 
+  # Returns the ids of the given groups and of their members as strings,
+  # fetching the members of all the groups with a single query
+  def group_and_member_ids(groups)
+    group_ids = groups.map(&:id)
+    return [] if group_ids.empty?
+
+    user_ids = User.where(
+      "#{User.table_name}.id IN (SELECT gu.user_id" \
+        " FROM #{User.table_name_prefix}groups_users#{User.table_name_suffix} gu" \
+        " WHERE gu.group_id IN (?))",
+      group_ids
+    ).pluck(:id)
+    (group_ids + user_ids).uniq.compact.sort.collect(&:to_s)
+  end
+  private :group_and_member_ids
+
   def sql_for_author_role_field(field, operator, value)
     role_cond =
       if value.any?