diff --git a/src/core/ngx_output_chain.c b/src/core/ngx_output_chain.c
index 3d5ae1db5..ecb0f31bf 100644
--- a/src/core/ngx_output_chain.c
+++ b/src/core/ngx_output_chain.c
@@ -505,8 +505,8 @@ ngx_output_chain_copy_buf(ngx_output_chain_ctx_t *ctx)
 
         if (n != size) {
             ngx_log_error(NGX_LOG_ALERT, ctx->pool->log, 0,
-                          ngx_read_file_n " read only %z of %O from file",
-                          n, size);
+                          ngx_read_file_n " read only %z of %O from \"%s\"",
+                          n, size, src->file->name.data);
             if (n == 0) {
                 return NGX_ERROR;
             }