diff --git a/escpos/escpos.py b/escpos/escpos.py
index 64b31fe..1b90b91 100644
--- a/escpos/escpos.py
+++ b/escpos/escpos.py
@@ -492,17 +492,21 @@ class Escpos(object):
             self._raw(TXT_2WIDTH)
         elif width == 1 and height == 1:
             self._raw(TXT_NORMAL)
-        else:
+        elif width >= 1 and width <= 8 and height >= 1 and height <= 8 and isinstance(width, int) and isinstance(height, int):
             self._raw(TXT_SIZE + chr(TXT_WIDTH[width] + TXT_HEIGHT[height]))
-        # Type
+        else:
+            raise SetVariableError()
+        # Upside down
         if flip == True:
             self._raw(TXT_FLIP_ON)
         else:
             self._raw(TXT_FLIP_OFF)
+        # Smoothing
         if smooth == True:
             self._raw(TXT_SMOOTH_ON)
         else:
             self._raw(TXT_SMOOTH_OFF)
+        # Type
         if text_type.upper() == "B":
             self._raw(TXT_BOLD_ON)
             self._raw(TXT_UNDERL_OFF)
diff --git a/escpos/exceptions.py b/escpos/exceptions.py
index e91ed5e..56a30a4 100644
--- a/escpos/exceptions.py
+++ b/escpos/exceptions.py
@@ -12,6 +12,7 @@ Result/Exit codes:
     - `70` = Invalid number of tab positions :py:exc:`~escpos.exceptions.TabPosError`
     - `80` = Invalid char code :py:exc:`~escpos.exceptions.CharCodeError`
     - `90` = USB device not found :py:exc:`~escpos.exceptions.USBNotFoundError`
+    - `100` = Set variable out of range :py:exc:`~escpos.exceptions.SetVariableError`
 
 :author: `Manuel F Martinez <manpaz@bashlinux.com>`_ and others
 :organization: Bashlinux and `python-escpos <https://github.com/python-escpos>`_
@@ -167,3 +168,18 @@ class USBNotFoundError(Error):
 
     def __str__(self):
         return "USB device not found"
+
+
+class SetVariableError(Error):
+    """ A set method variable was out of range
+
+    Check set variables against minimum and maximum values
+    Ths returncode for this exception is `100`.
+    """
+    def __init__(self, msg=""):
+        Error.__init__(self, msg)
+        self.msg = msg
+        self.resultcode = 100
+
+    def __str__(self):
+        return "Set variable out of range"