diff --git a/src/os/unix/ngx_files.c b/src/os/unix/ngx_files.c
index 76b86a0..7b9d4e4 100644
--- a/src/os/unix/ngx_files.c
+++ b/src/os/unix/ngx_files.c
@@ -25,13 +25,15 @@
 
 #else
 
-    if (file->offset != offset) {
+    if (file->sys_offset != offset) {
         if (lseek(file->fd, offset, SEEK_SET) == -1) {
             ngx_log_error(NGX_LOG_CRIT, file->log, ngx_errno, "lseek() failed");
             return NGX_ERROR;
         }
     }
 
+    file->sys_offset = offset;
+
     n = read(file->fd, buf, size);
 
     if (n == -1) {
@@ -39,6 +41,8 @@
         return NGX_ERROR;
     }
 
+    file->sys_offset += n;
+
 #endif
 
     file->offset += n;
@@ -68,13 +72,15 @@
 
 #else
 
-    if (file->offset != offset) {
+    if (file->sys_offset != offset) {
         if (lseek(file->fd, offset, SEEK_SET) == -1) {
             ngx_log_error(NGX_LOG_CRIT, file->log, ngx_errno, "lseek() failed");
             return NGX_ERROR;
         }
     }
 
+    file->sys_offset = offset;
+
     n = write(file->fd, buf, size);
 
     if (n == -1) {
@@ -88,6 +94,8 @@
         return NGX_ERROR;
     }
 
+    file->sys_offset += n;
+
 #endif
 
     file->offset += n;
@@ -150,6 +158,8 @@
         }
     }
 
+    file->sys_offset = offset;
+
     n = writev(file->fd, io.elts, io.nelts);
 
     if (n == -1) {
@@ -163,6 +173,7 @@
         return NGX_ERROR;
     }
 
+    file->sys_offset += n;
     file->offset += n;
 
     return n;