diff --git a/src/shrpx.cc b/src/shrpx.cc
index 26326e2f..7160bf6c 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -2030,11 +2030,13 @@ int main(int argc, char **argv) {
   }
 
   if (conf_exists(get_config()->conf_path.get())) {
-    if (load_config(get_config()->conf_path.get()) == -1) {
+    std::set<std::string> include_set;
+    if (load_config(get_config()->conf_path.get(), include_set) == -1) {
       LOG(FATAL) << "Failed to load configuration from "
                  << get_config()->conf_path.get();
       exit(EXIT_FAILURE);
     }
+    assert(include_set.empty());
   }
 
   if (argc - optind >= 2) {
@@ -2046,11 +2048,18 @@ int main(int argc, char **argv) {
   // parsing option values.
   reopen_log_files();
 
-  for (size_t i = 0, len = cmdcfgs.size(); i < len; ++i) {
-    if (parse_config(cmdcfgs[i].first, cmdcfgs[i].second) == -1) {
-      LOG(FATAL) << "Failed to parse command-line argument.";
-      exit(EXIT_FAILURE);
+  {
+    std::set<std::string> include_set;
+
+    for (size_t i = 0, len = cmdcfgs.size(); i < len; ++i) {
+      if (parse_config(cmdcfgs[i].first, cmdcfgs[i].second, include_set) ==
+          -1) {
+        LOG(FATAL) << "Failed to parse command-line argument.";
+        exit(EXIT_FAILURE);
+      }
     }
+
+    assert(include_set.empty());
   }
 
   if (get_config()->accesslog_syslog || get_config()->errorlog_syslog) {
diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index 49ad49a8..6a978b1c 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -505,7 +505,8 @@ void parse_mapping(const DownstreamAddr &addr, const char *src) {
 }
 } // namespace
 
-int parse_config(const char *opt, const char *optarg) {
+int parse_config(const char *opt, const char *optarg,
+                 std::set<std::string> &included_set) {
   char host[NI_MAXHOST];
   uint16_t port;
 
@@ -1220,7 +1221,20 @@ int parse_config(const char *opt, const char *optarg) {
   }
 
   if (util::strieq(opt, SHRPX_OPT_INCLUDE)) {
-    return load_config(optarg);
+    if (included_set.count(optarg)) {
+      LOG(ERROR) << opt << ": " << optarg << " has already been included";
+      return -1;
+    }
+
+    included_set.emplace(optarg);
+    auto rv = load_config(optarg, included_set);
+    included_set.erase(optarg);
+
+    if (rv != 0) {
+      return -1;
+    }
+
+    return 0;
   }
 
   if (util::strieq(opt, "conf")) {
@@ -1234,7 +1248,7 @@ int parse_config(const char *opt, const char *optarg) {
   return -1;
 }
 
-int load_config(const char *filename) {
+int load_config(const char *filename, std::set<std::string> &include_set) {
   std::ifstream in(filename, std::ios::binary);
   if (!in) {
     LOG(ERROR) << "Could not open config file " << filename;
@@ -1258,7 +1272,7 @@ int load_config(const char *filename) {
     }
     line[i] = '\0';
     auto s = line.c_str();
-    if (parse_config(s, s + i + 1) == -1) {
+    if (parse_config(s, s + i + 1, include_set) == -1) {
       return -1;
     }
   }
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index 5f23c5b3..ea455f02 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -42,6 +42,7 @@
 #include <cstdio>
 #include <vector>
 #include <memory>
+#include <set>
 
 #include <openssl/ssl.h>
 
@@ -379,13 +380,16 @@ void create_config();
 
 // Parses option name |opt| and value |optarg|.  The results are
 // stored into statically allocated Config object. This function
-// returns 0 if it succeeds, or -1.
-int parse_config(const char *opt, const char *optarg);
+// returns 0 if it succeeds, or -1.  The |included_set| contains the
+// all paths already included while processing this configuration, to
+// avoid loop in --include option.
+int parse_config(const char *opt, const char *optarg,
+                 std::set<std::string> &included_set);
 
 // Loads configurations from |filename| and stores them in statically
 // allocated Config object. This function returns 0 if it succeeds, or
-// -1.
-int load_config(const char *filename);
+// -1.  See parse_config() for |include_set|.
+int load_config(const char *filename, std::set<std::string> &include_set);
 
 // Read passwd from |filename|
 std::string read_passwd_from_file(const char *filename);