diff --git a/src/sfnt/sfobjs.c b/src/sfnt/sfobjs.c
index f9d4d3858..9771c35df 100644
--- a/src/sfnt/sfobjs.c
+++ b/src/sfnt/sfobjs.c
@@ -566,7 +566,7 @@
     face_index = FT_ABS( face_instance_index ) & 0xFFFF;
 
     /* value -(N+1) requests information on index N */
-    if ( face_instance_index < 0 )
+    if ( face_instance_index < 0 && face_index > 0 )
       face_index--;
 
     if ( face_index >= face->ttc_header.count )
diff --git a/src/sfnt/sfwoff2.c b/src/sfnt/sfwoff2.c
index cb1e0664a..165b875e5 100644
--- a/src/sfnt/sfwoff2.c
+++ b/src/sfnt/sfwoff2.c
@@ -2085,7 +2085,7 @@
     /* Validate requested face index. */
     *num_faces = woff2.num_fonts;
     /* value -(N+1) requests information on index N */
-    if ( *face_instance_index < 0 )
+    if ( *face_instance_index < 0 && face_index > 0 )
       face_index--;
 
     if ( face_index >= woff2.num_fonts )