diff --git a/src/base/ftobjs.c b/src/base/ftobjs.c
index 745ad196fdef78069e35646cfcb5e8b883ec51a9..784e3ab4e27186681f75caf4646b038c9f77167d 100644
--- a/src/base/ftobjs.c
+++ b/src/base/ftobjs.c
@@ -2407,6 +2407,15 @@
 #endif
 
 
+    /* only use lower 31 bits together with sign bit */
+    if( face_index > 0 )
+      face_index &= 0x7FFFFFFFL;
+    else
+    {
+      face_index &= 0x7FFFFFFFL;
+      face_index = -face_index;
+    }
+
 #ifdef FT_DEBUG_LEVEL_TRACE
     FT_TRACE3(( "FT_Open_Face: " ));
     if ( face_index < 0 )