diff --git a/include/custom.h b/include/custom.h
new file mode 100644
index 0000000..0bb83df
--- /dev/null
+++ b/include/custom.h
@@ -0,0 +1,41 @@
+#ifndef LIBABACUS_CUSTOM_H
+#define LIBABACUS_CUSTOM_H
+
+/**
+ * A function pointer that is called
+ * to execute a certain type of function.
+ */
+typedef void(*libab_function_ptr)();
+
+/**
+ * A struct that holds informatiion
+ * about an operator that has been
+ * registered with libabacus.
+ */
+struct libab_operator_s {
+    /**
+     * The precedence of the operator.
+     */
+    int precedence;
+    /**
+     * The functionality of the operator.
+     */
+    libab_function_ptr function;
+};
+
+/**
+ * A struct that holds information
+ * about an function that has been
+ * registered with libabacus.
+ */
+struct libab_function_s {
+    /**
+     * The functionality of the function.
+     */
+    libab_function_ptr function;
+};
+
+typedef struct libab_operator_s libab_operator;
+typedef struct libab_function_s libab_function;
+
+#endif
diff --git a/include/libabacus.h b/include/libabacus.h
index 2719834..5880b76 100644
--- a/include/libabacus.h
+++ b/include/libabacus.h
@@ -6,41 +6,7 @@
 #include "table.h"
 #include "parser.h"
 #include "result.h"
-
-/**
- * A function pointer that is called
- * to execute a certain type of function.
- */
-typedef void(*libab_function_ptr)();
-
-/**
- * A struct that holds informatiion
- * about an operator that has been
- * registered with libabacus.
- */
-struct libab_operator_s {
-    /**
-     * The precedence of the operator.
-     */
-    int precedence;
-    /**
-     * The functionality of the operator.
-     */
-    libab_function_ptr function;
-};
-
-/**
- * A struct that holds information
- * about an function that has been
- * registered with libabacus.
- */
-struct libab_function_s {
-    /**
-     * The functionality of the function.
-     */
-    libab_function_ptr function;
-};
-
+#include "custom.h"
 
 /**
  * The main struct of libabacus,
@@ -65,8 +31,6 @@ struct libab_s {
     libab_table table;
 };
 
-typedef struct libab_operator_s libab_operator;
-typedef struct libab_function_s libab_function;
 typedef struct libab_s libab;
 
 /**