diff --git a/ext/liquid/block.c b/ext/liquid/block.c
index 18927a3..2ffeddd 100644
--- a/ext/liquid/block.c
+++ b/ext/liquid/block.c
@@ -1,6 +1,5 @@
 #include "liquid_ext.h"
 
-extern VALUE mLiquid, cLiquidTokenizer, cLiquidTag, cLiquidTemplate, cLiquidVariable;
 VALUE cLiquidBlock;
 ID intern_assert_missing_delimitation, intern_block_delimiter, intern_is_blank, intern_new,
    intern_new_with_options, intern_tags, intern_unknown_tag, intern_unterminated_tag,
@@ -46,14 +45,7 @@ static bool parse_tag(struct liquid_tag *tag, char *token, long token_length)
 
 static VALUE rb_parse_body(VALUE self, VALUE tokenizerObj)
 {
-    Check_Type(tokenizerObj, T_DATA);
-    if (RBASIC_CLASS(tokenizerObj) != cLiquidTokenizer) {
-        rb_raise(rb_eTypeError, "wrong argument type %s (expected %s)",
-                 rb_obj_classname(tokenizerObj),
-                 rb_class2name(cLiquidTokenizer));
-    }
-    struct liquid_tokenizer *tokenizer;
-    Data_Get_Struct(tokenizerObj, struct liquid_tokenizer, tokenizer);
+    struct liquid_tokenizer *tokenizer = LIQUID_TOKENIZER_GET_STRUCT(tokenizerObj);
 
     bool blank = true;
     VALUE nodelist = rb_iv_get(self, "@nodelist");
diff --git a/ext/liquid/block.h b/ext/liquid/block.h
index ab4273c..ddb8a08 100644
--- a/ext/liquid/block.h
+++ b/ext/liquid/block.h
@@ -3,4 +3,6 @@
 
 void init_liquid_block();
 
+extern VALUE cLiquidBlock;
+
 #endif
diff --git a/ext/liquid/liquid_ext.h b/ext/liquid/liquid_ext.h
index 796ae99..3eba3ae 100644
--- a/ext/liquid/liquid_ext.h
+++ b/ext/liquid/liquid_ext.h
@@ -7,5 +7,9 @@
 
 #include "tokenizer.h"
 #include "block.h"
+#include "utils.h"
+
+extern VALUE mLiquid;
+extern VALUE cLiquidTemplate, cLiquidTag, cLiquidVariable;
 
 #endif
diff --git a/ext/liquid/tokenizer.c b/ext/liquid/tokenizer.c
index 26e2368..a70efa3 100644
--- a/ext/liquid/tokenizer.c
+++ b/ext/liquid/tokenizer.c
@@ -1,7 +1,6 @@
 #include "liquid_ext.h"
 
 VALUE cLiquidTokenizer;
-extern VALUE mLiquid;
 
 static void free_tokenizer(void *ptr)
 {
diff --git a/ext/liquid/tokenizer.h b/ext/liquid/tokenizer.h
index 83b7351..530c5e4 100644
--- a/ext/liquid/tokenizer.h
+++ b/ext/liquid/tokenizer.h
@@ -1,6 +1,8 @@
 #ifndef LIQUID_TOKENIZER_H
 #define LIQUID_TOKENIZER_H
 
+extern VALUE cLiquidTokenizer;
+
 enum token_type {
     TOKEN_NONE,
     TOKEN_INVALID,
@@ -23,4 +25,6 @@ struct liquid_tokenizer {
 void init_liquid_tokenizer();
 void liquid_tokenizer_next(struct liquid_tokenizer *tokenizer, struct token *token);
 
+#define LIQUID_TOKENIZER_GET_STRUCT(obj) ((struct liquid_tokenizer *)obj_get_data_ptr(obj, cLiquidTokenizer))
+
 #endif
diff --git a/ext/liquid/utils.c b/ext/liquid/utils.c
new file mode 100644
index 0000000..c68cbfa
--- /dev/null
+++ b/ext/liquid/utils.c
@@ -0,0 +1,21 @@
+#include <ruby.h>
+
+void raise_type_error(VALUE expected, VALUE got)
+{
+    rb_raise(rb_eTypeError, "wrong argument type %s (expected %s)",
+                             rb_class2name(got), rb_class2name(expected));
+}
+
+void check_class(VALUE obj, int type, VALUE klass)
+{
+    Check_Type(obj, type);
+    VALUE obj_klass = RBASIC_CLASS(obj);
+    if (obj_klass != klass)
+        raise_type_error(klass, obj_klass);
+}
+
+void *obj_get_data_ptr(VALUE obj, VALUE klass)
+{
+    check_class(obj, T_DATA, klass);
+    return DATA_PTR(obj);
+}
diff --git a/ext/liquid/utils.h b/ext/liquid/utils.h
new file mode 100644
index 0000000..675a1e3
--- /dev/null
+++ b/ext/liquid/utils.h
@@ -0,0 +1,8 @@
+#ifndef LIQUID_UTILS_H
+#define LIQUID_UTILS_H
+
+void raise_type_error(VALUE expected, VALUE got);
+void check_class(VALUE klass);
+void *obj_get_data_ptr(VALUE obj, VALUE klass);
+
+#endif