--- JSON-XS/XS.xs	2018/08/28 16:16:17	1.133
+++ JSON-XS/XS.xs	2018/11/15 20:13:03	1.134
@@ -52,7 +52,7 @@
 
 #define F_PRETTY    F_INDENT | F_SPACE_BEFORE | F_SPACE_AFTER
 
-#define INIT_SIZE   32 // initial scalar size to be allocated
+#define INIT_SIZE   64 // initial scalar size to be allocated
 #define INDENT_STEP 3  // spaces per indentation level
 
 #define SHORT_STRING_LEN 16384 // special-case strings of up to this size
@@ -790,7 +790,6 @@
           dSP;
 
           ENTER; SAVETMPS;
-          SAVESTACK_POS ();
           PUSHMARK (SP);
           EXTEND (SP, 2);
           // we re-bless the reference to get overload and other niceties right
@@ -812,12 +811,18 @@
           encode_ch (enc, ')');
           encode_ch (enc, '[');
 
-          while (count)
+          if (count)
             {
-              encode_sv (enc, SP[1 - count--]);
+              int i;
 
-              if (count)
-                encode_ch (enc, ',');
+              for (i = 0; i < count - 1; ++i)
+                {
+                  encode_sv (enc, SP[i + 1 - count]);
+                  encode_ch (enc, ',');
+                }
+
+              encode_sv (enc, TOPs);
+              SP -= count;
             }
 
           encode_ch (enc, ']');
@@ -1518,7 +1523,6 @@
               int count;
 
               ENTER; SAVETMPS;
-              SAVESTACK_POS ();
               PUSHMARK (SP);
               XPUSHs (HeVAL (he));
               sv_2mortal (sv);
@@ -1531,6 +1535,8 @@
                   FREETMPS; LEAVE;
                   return sv;
                 }
+              else if (count)
+                croak ("filter_json_single_key_object callbacks must not return more than one scalar");
 
               SvREFCNT_inc (sv);
               FREETMPS; LEAVE;
@@ -1543,7 +1549,6 @@
           int count;
 
           ENTER; SAVETMPS;
-          SAVESTACK_POS ();
           PUSHMARK (SP);
           XPUSHs (sv_2mortal (sv));
 
@@ -1555,6 +1560,8 @@
               FREETMPS; LEAVE;
               return sv;
             }
+          else if (count)
+            croak ("filter_json_object callbacks must not return more than one scalar");
 
           SvREFCNT_inc (sv);
           FREETMPS; LEAVE;