diff --git a/src/permission/fs_permission.cc b/src/permission/fs_permission.cc
index fadf75968c779d..7a073f99a49440 100644
--- a/src/permission/fs_permission.cc
+++ b/src/permission/fs_permission.cc
@@ -56,7 +56,7 @@ bool is_tree_granted(node::permission::FSPermission::RadixTree* granted_tree,
   // is UNC file path
   if (param.rfind("\\\\", 0) == 0) {
     // return lookup with normalized param
-    int starting_pos = 4;  // "\\?\"
+    size_t starting_pos = 4;  // "\\?\"
     if (param.rfind("\\\\?\\UNC\\") == 0) {
       starting_pos += 4;  // "UNC\"
     }
@@ -176,7 +176,7 @@ bool FSPermission::RadixTree::Lookup(const std::string_view& s,
   if (current_node->children.size() == 0) {
     return when_empty_return;
   }
-  unsigned int parent_node_prefix_len = current_node->prefix.length();
+  size_t parent_node_prefix_len = current_node->prefix.length();
   const std::string path(s);
   auto path_len = path.length();
 
@@ -202,10 +202,10 @@ bool FSPermission::RadixTree::Lookup(const std::string_view& s,
 void FSPermission::RadixTree::Insert(const std::string& path) {
   FSPermission::RadixTree::Node* current_node = root_node_;
 
-  unsigned int parent_node_prefix_len = current_node->prefix.length();
-  int path_len = path.length();
+  size_t parent_node_prefix_len = current_node->prefix.length();
+  size_t path_len = path.length();
 
-  for (int i = 1; i <= path_len; ++i) {
+  for (size_t i = 1; i <= path_len; ++i) {
     bool is_wildcard_node = path[i - 1] == '*';
     bool is_last_char = i == path_len;
 
diff --git a/src/permission/fs_permission.h b/src/permission/fs_permission.h
index 80374a08c75d26..74b1440536652a 100644
--- a/src/permission/fs_permission.h
+++ b/src/permission/fs_permission.h
@@ -45,8 +45,8 @@ class FSPermission final : public PermissionBase {
         }
 
         // swap prefix
-        unsigned int i = 0;
-        unsigned int prefix_len = prefix.length();
+        size_t i = 0;
+        size_t prefix_len = prefix.length();
         for (; i < child->prefix.length(); ++i) {
           if (i > prefix_len || prefix[i] != child->prefix[i]) {
             std::string parent_prefix = child->prefix.substr(0, i);
@@ -72,7 +72,7 @@ class FSPermission final : public PermissionBase {
         return wildcard_child;
       }
 
-      Node* NextNode(const std::string& path, unsigned int idx) {
+      Node* NextNode(const std::string& path, size_t idx) {
         if (idx >= path.length()) {
           return nullptr;
         }
@@ -83,8 +83,8 @@ class FSPermission final : public PermissionBase {
         }
         auto child = it->second;
         // match prefix
-        unsigned int prefix_len = child->prefix.length();
-        for (unsigned int i = 0; i < path.length(); ++i) {
+        size_t prefix_len = child->prefix.length();
+        for (size_t i = 0; i < path.length(); ++i) {
           if (i >= prefix_len || child->prefix[i] == '*') {
             return child;
           }