diff --git a/tools/json2cbor/json2cbor.c b/tools/json2cbor/json2cbor.c
index 090ee158..bb35108b 100644
--- a/tools/json2cbor/json2cbor.c
+++ b/tools/json2cbor/json2cbor.c
@@ -328,15 +328,17 @@ CborError decode_json(cJSON *json, CborEncoder *encoder)
         err = cbor_encode_double(encoder, json->valuedouble);
 
         if (err == CborErrorOutOfMemory) {
-            buffersize += 1024;
-            uint8_t *newbuffer = realloc(buffer, buffersize);
+            ptrdiff_t offset = cbor_encoder_get_buffer_size(&container, buffer);
+            size_t newbuffersize = buffersize + 1024;
+            uint8_t *newbuffer = realloc(buffer, newbuffersize);
             if (newbuffer == NULL)
                 return err;
 
             *encoder = container;   // restore state
-            encoder->data.ptr = newbuffer + (container.data.ptr - buffer);
-            encoder->end = newbuffer + buffersize;
+            encoder->data.ptr = newbuffer + offset;
+            encoder->end = newbuffer + newbuffersize;
             buffer = newbuffer;
+            buffersize = newbuffersize;
             goto encode_double;
         }
         return err;