diff --git a/Lib/fontTools/varLib/__init__.py b/Lib/fontTools/varLib/__init__.py
index d5a8daccc..22e244112 100644
--- a/Lib/fontTools/varLib/__init__.py
+++ b/Lib/fontTools/varLib/__init__.py
@@ -563,11 +563,11 @@ def _get_advance_metrics(
 ):
     vhAdvanceDeltasAndSupports = {}
     vOrigDeltasAndSupports = {}
-    # HACK: we treat width 65535 and lsb -32768 as sentinel values to signal that a
-    # glyph from a non-default master should not participate in computing {H,V}VAR,
+    # HACK: we treat width 65535 and lsb 0 as sentinel values to signal that a glyph
+    # from a non-default master should not participate in computing {H,V}VAR,
     # as if it were missing. Allows to variate other glyph-related data independently
     # from glyph metrics
-    sparse_metrics = (0xFFFF, -0x8000)
+    sparse_metrics = (0xFFFF, 0)
     for glyph in glyphOrder:
         vhAdvances = [
             metrics[glyph][0]
diff --git a/Tests/varLib/data/master_sparse_cff2_empty/SparseCFF-Medium.ttx b/Tests/varLib/data/master_sparse_cff2_empty/SparseCFF-Medium.ttx
index 41cf6ce07..1b583bd33 100644
--- a/Tests/varLib/data/master_sparse_cff2_empty/SparseCFF-Medium.ttx
+++ b/Tests/varLib/data/master_sparse_cff2_empty/SparseCFF-Medium.ttx
@@ -93,7 +93,7 @@
   </CFF>
 
   <hmtx>
-    <mtx name=".notdef" width="65535" lsb="-32768"/>
+    <mtx name=".notdef" width="65535" lsb="0"/>
     <mtx name="e" width="600" lsb="40"/>
   </hmtx>