diff --git a/src/hb-cff2-interp-cs.hh b/src/hb-cff2-interp-cs.hh
index 672e67c94..ef680f0e9 100644
--- a/src/hb-cff2-interp-cs.hh
+++ b/src/hb-cff2-interp-cs.hh
@@ -247,6 +247,7 @@ struct CFF2CSOpSet : CSOpSet<BlendArg, OPSET, CFF2CSInterpEnv, PARAM, PATH>
   static inline void process_vsindex (CFF2CSInterpEnv &env, PARAM& param)
   {
     env.process_vsindex ();
+    env.clear_args ();
   }
 
   private:
diff --git a/src/hb-ot-cff1-table.hh b/src/hb-ot-cff1-table.hh
index bc67e49b5..820404ed6 100644
--- a/src/hb-ot-cff1-table.hh
+++ b/src/hb-ot-cff1-table.hh
@@ -64,6 +64,8 @@ struct Encoding0 {
 
   inline hb_codepoint_t get_code (hb_codepoint_t glyph) const
   {
+    assert (glyph > 0);
+    glyph--;
     if (glyph < nCodes)
     {
       return (hb_codepoint_t)codes[glyph];
@@ -106,6 +108,8 @@ struct Encoding1 {
 
   inline hb_codepoint_t get_code (hb_codepoint_t glyph) const
   {
+    assert (glyph > 0);
+    glyph--;
     for (unsigned int i = 0; i < nRanges; i++)
     {
       if (glyph <= ranges[i].nLeft)
diff --git a/src/hb-ot-cff2-table.hh b/src/hb-ot-cff2-table.hh
index 04d9e2b38..1b01c1cfe 100644
--- a/src/hb-ot-cff2-table.hh
+++ b/src/hb-ot-cff2-table.hh
@@ -347,6 +347,7 @@ struct CFF2PrivateDictOpSet : DictOpSet
       case OpCode_vsindexdict:
         env.process_vsindex ();
         dictval.ivs = env.get_ivs ();
+        env.clear_args ();
         break;
       case OpCode_blenddict:
         break;