diff --git a/include/common/fzl_opcodes.h b/include/common/fzl_opcodes.h
index 8603d3f..fb6fc2d 100644
--- a/include/common/fzl_opcodes.h
+++ b/include/common/fzl_opcodes.h
@@ -20,8 +20,9 @@ typedef enum
   FZL_OPCODE_JMP = 0xF20001, // Jump to specified IP address
   FZL_OPCODE_JZ  = 0xF20002, // Jump if top value in dstack is zero
 
-  FZL_OPCODE_CALL = 0xF30001, // Call function
-  FZL_OPCODE_RET  = 0xF30002, // Return from function
+  FZL_OPCODE_CALL        = 0xF30001, // Call function
+  FZL_OPCODE_RET         = 0xF30002, // Return from function
+  FZL_OPCODE_CALL_EXTERN = 0xF30003, // Call external function
 
   FZL_OPCODE_ALLOC_OBJECT  = 0xFA0001, // Allocate N slots
   FZL_OPCODE_GET_FIELD     = 0xFA0002, // Get field N of an object at dstack
diff --git a/include/compiler/utils/fzl_extern.h b/include/compiler/utils/fzl_extern.h
new file mode 100644
index 0000000..2fe0815
--- /dev/null
+++ b/include/compiler/utils/fzl_extern.h
@@ -0,0 +1,16 @@
+#ifndef FZL_EXTERN_H
+#define FZL_EXTERN_H
+
+// Library symbol descriptor
+typedef struct
+{
+  //
+} fzl_extern_item_t;
+
+// External library descriptor
+typedef struct
+{
+  //
+} fzl_extern_lib_t;
+
+#endif // FZL_EXTERN_H
diff --git a/src/compiler/analyzer/utility.c b/src/compiler/analyzer/utility.c
index d6a7401..6ba3c99 100644
--- a/src/compiler/analyzer/utility.c
+++ b/src/compiler/analyzer/utility.c
@@ -1,6 +1,8 @@
 #include <common/fzl_types.h>
 #include <compiler/fzl_analyzer.h>
+#include <compiler/fzl_parser.h>
 #include <compiler/fzl_token.h>
+#include <compiler/internals/analyzer.h>
 #include <compiler/utils/fzl_symtable.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -101,7 +103,21 @@ fzl_type_t an_toktotype(fzl_analyzer_t *analyzer, fzl_token_t *tok,
     if (sym_found)
       *sym_found = found;
 
-    return found ? sym.type : FZL_TYPE_NULL;
+    if (found && sym.node->type == FZL_NODETYPE_CLASS)
+      return FZL_TYPE_OBJECT;
+
+    if (found && sym.node->type != FZL_NODETYPE_CLASS &&
+        sym.node->type != FZL_NODETYPE_TYPEDEF)
+    {
+      snprintf(an_problem, sizeof(an_problem), "cannot use '%s' as type",
+               sym.name);
+      an_push_error(analyzer, sym.node->token, an_problem);
+      return FZL_TYPE_NULL;
+    }
+
+    return (found || (tok->value && strcmp(tok->value, "null") == 0))
+               ? sym.type
+               : FZL_TYPE_NULL;
   }
 
   if (sym_found)
diff --git a/src/compiler/fzl_walker.c b/src/compiler/fzl_walker.c
index d7f34d6..b392576 100644
--- a/src/compiler/fzl_walker.c
+++ b/src/compiler/fzl_walker.c
@@ -203,6 +203,9 @@ fzl_walk_res_t walk(fzl_walker_t *walker, fzl_node_t *node)
   {
     switch (node->type)
     {
+      case FZL_NODETYPE_TYPEDEF:
+        break;
+
       case FZL_NODETYPE_FMT_STRING:
       {
         for (size_t i = 0; i < node->list.entry_count; i++)
diff --git a/src/compiler/main.c b/src/compiler/main.c
index 5c7e64c..49f1adc 100644
--- a/src/compiler/main.c
+++ b/src/compiler/main.c
@@ -123,7 +123,7 @@ int main(int argc, char **argv)
     printf("%sok%s!\n", FZL_COK, FZL_CRST);
     fzl_debug_print_ast(parser->root);
     printf("%s> building%s\n", FZL_CDEBUG, FZL_CRST);
-    printf("%s-> analyzing AST...%s\n", FZL_CDEBUG, FZL_CRST);
+    printf("%s-> analyzing AST...%s", FZL_CDEBUG, FZL_CRST);
   }
 
   fzl_analyzer_t *analyzer = fzl_mkanalyzer(parser->root);