diff --git a/cfg/windows.cfg b/cfg/windows.cfg
index 5d391ea8f..da6712ccd 100644
--- a/cfg/windows.cfg
+++ b/cfg/windows.cfg
@@ -4871,6 +4871,28 @@ HFONT CreateFont(
       <not-bool/>
     </arg>
   </function>
+  <!-- int _tolower(int c); -->
+  <function name="_tolower">
+    <use-retval/>
+    <returnValue type="int"/>
+    <noreturn>false</noreturn>
+    <leak-ignore/>
+    <arg nr="1">
+      <not-uninit/>
+      <valid>0:255</valid>
+    </arg>
+  </function>
+  <!-- int _toupper(int c); -->
+  <function name="_toupper">
+    <use-retval/>
+    <returnValue type="int"/>
+    <noreturn>false</noreturn>
+    <leak-ignore/>
+    <arg nr="1">
+      <not-uninit/>
+      <valid>0:255</valid>
+    </arg>
+  </function>  
   <podtype name="LARGE_INTEGER" sign="s" size="8"/>
   <podtype name="POINTER_SIGNED" sign="s"/>
   <podtype name="POINTER_UNSIGNED" sign="u"/>