diff --git a/src/os_unix.c b/src/os_unix.c
index 4dd38ce..c09638f 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -3222,8 +3222,9 @@
 
     /*
      * 2. get size from environment
+     *    When being POSIX compliant this overrules the ioctl() values!
      */
-    if (columns == 0 || rows == 0)
+    if (columns == 0 || rows == 0 || getenv("VIM_POSIX") != NULL)
     {
 	if ((p = (char_u *)getenv("LINES")))
 	    rows = atoi((char *)p);