diff --git a/src/eval_cps.c b/src/eval_cps.c
index 02b9779f..d5f64274 100644
--- a/src/eval_cps.c
+++ b/src/eval_cps.c
@@ -3571,6 +3571,8 @@ static void cont_read_next_token(eval_context_t *ctx) {
             error_ctx(ENC_SYM_FATAL_ERROR);
           }
           symbol_id = ext_id + EXTENSION_SYMBOLS_START;
+        } else {
+          error_ctx(ENC_SYM_MERROR);
         }
       } else {
         if (ctx->flags & EVAL_CPS_CONTEXT_FLAG_CONST_SYMBOL_STRINGS &&
diff --git a/src/extensions.c b/src/extensions.c
index fbc6c1a5..869e9345 100644
--- a/src/extensions.c
+++ b/src/extensions.c
@@ -48,6 +48,7 @@ int lbm_extensions_init(lbm_extension_t *extension_storage, lbm_uint extension_s
     extension_storage[i].fptr = lbm_extensions_default;
   }
 
+  ext_num = 0;
   next_extension_ix = 0;
   ext_max = (lbm_uint)extension_storage_size;