diff --git a/cfg/std.cfg b/cfg/std.cfg
index 7af867d89..56831ad1d 100644
--- a/cfg/std.cfg
+++ b/cfg/std.cfg
@@ -21,6 +21,7 @@
     <use-retval/>
     <pure/>
     <noreturn>false</noreturn>
+    <returnValue>arg1&gt;0?arg1:-arg1</returnValue>
     <leak-ignore/>
     <arg nr="1">
       <not-uninit/>
diff --git a/cfg/windows.cfg b/cfg/windows.cfg
index c968bd8b2..9dd78b907 100644
--- a/cfg/windows.cfg
+++ b/cfg/windows.cfg
@@ -2656,4 +2656,16 @@ HFONT CreateFont(
       <not-uninit/>
     </arg>
   </function>
+  <!--__int64 _abs64( __int64 n);-->
+  <function name="_abs64">
+    <use-retval/>
+    <pure/>
+    <noreturn>false</noreturn>
+    <leak-ignore/>
+    <returnValue>arg1&gt;0?arg1:-arg1</returnValue>
+    <arg nr="1">
+      <not-uninit/>
+      <not-bool/>
+    </arg>
+  </function>
 </def>