diff --git a/res/content/base/package.json b/res/content/base/package.json
index a9f081fa..bd8c1c2a 100644
--- a/res/content/base/package.json
+++ b/res/content/base/package.json
@@ -1,6 +1,6 @@
 {
     "id": "base",
     "title": "Base",
-    "version": "0.16",
+    "version": "0.18",
     "description": "basic content package"
 }
diff --git a/src/constants.h b/src/constants.h
index 1c4eecfd..dd5e56e0 100644
--- a/src/constants.h
+++ b/src/constants.h
@@ -7,6 +7,9 @@
 const int ENGINE_VERSION_MAJOR = 0;
 const int ENGINE_VERSION_MINOR = 18;
 
+const int BLOCK_AIR = 0;
+const int ITEM_EMPTY = 0;
+
 const int CHUNK_W = 16;
 const int CHUNK_H = 256;
 const int CHUNK_D = 16;
diff --git a/src/content/Content.cpp b/src/content/Content.cpp
index ca2ce3cf..d808e48b 100644
--- a/src/content/Content.cpp
+++ b/src/content/Content.cpp
@@ -48,7 +48,7 @@ ItemDef* ContentBuilder::createItem(std::string id) {
 
 void ContentBuilder::checkIdentifier(std::string id) {
     contenttype result;
-    if ((checkContentType(id) != contenttype::none)) {
+    if (((result = checkContentType(id)) != contenttype::none)) {
         throw namereuse_error("name "+id+" is already used", result);
     }  
 }
diff --git a/src/core_defs.h b/src/core_defs.h
index 78aea0ef..5cdfbf2b 100644
--- a/src/core_defs.h
+++ b/src/core_defs.h
@@ -1,12 +1,12 @@
 #ifndef SRC_CORE_DEFS_H_
 #define SRC_CORE_DEFS_H_
 
-/* blocks and bindings used in engine code */
+#include <string>
 
-const int BLOCK_AIR = 0;
 
 const std::string TEXTURE_NOTFOUND = "notfound";
 
+/* bindings used in engine code */
 const std::string BIND_MOVE_FORWARD = "movement.forward";
 const std::string BIND_MOVE_BACK = "movement.back";
 const std::string BIND_MOVE_LEFT = "movement.left";