diff --git a/tools/include/dwarfs/tool/tool.h b/tools/include/dwarfs/tool/tool.h
index 040cf629..14fcda5c 100644
--- a/tools/include/dwarfs/tool/tool.h
+++ b/tools/include/dwarfs/tool/tool.h
@@ -35,10 +35,11 @@
 namespace dwarfs {
 
 struct logger_options;
-struct iolayer;
 
 namespace tool {
 
+struct iolayer;
+
 std::string
 tool_header(std::string_view tool_name, std::string_view extra_info = "");