diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index 6e31a2ade6..1bd3ecd5cf 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -4529,7 +4529,7 @@ ngx_http_core_limit_except(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
     ngx_http_core_loc_conf_t  *clcf;
 
     if (pclcf->limit_except) {
-        return "duplicate";
+        return "is duplicate";
     }
 
     pclcf->limit_except = 0xffffffff;
diff --git a/src/http/ngx_http_script.c b/src/http/ngx_http_script.c
index c1a0b4c560..cc4d679435 100644
--- a/src/http/ngx_http_script.c
+++ b/src/http/ngx_http_script.c
@@ -220,7 +220,7 @@ ngx_http_set_complex_value_slot(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
     cv = (ngx_http_complex_value_t **) (p + cmd->offset);
 
     if (*cv != NULL) {
-        return "duplicate";
+        return "is duplicate";
     }
 
     *cv = ngx_palloc(cf->pool, sizeof(ngx_http_complex_value_t));
diff --git a/src/stream/ngx_stream_script.c b/src/stream/ngx_stream_script.c
index ff8e655a65..aa555ca2c1 100644
--- a/src/stream/ngx_stream_script.c
+++ b/src/stream/ngx_stream_script.c
@@ -222,7 +222,7 @@ ngx_stream_set_complex_value_slot(ngx_conf_t *cf, ngx_command_t *cmd,
     cv = (ngx_stream_complex_value_t **) (p + cmd->offset);
 
     if (*cv != NULL) {
-        return "duplicate";
+        return "is duplicate";
     }
 
     *cv = ngx_palloc(cf->pool, sizeof(ngx_stream_complex_value_t));