diff --git a/include/custom.h b/include/custom.h
index 0bb83df..46eb0b5 100644
--- a/include/custom.h
+++ b/include/custom.h
@@ -17,6 +17,10 @@ struct libab_operator_s {
      * The precedence of the operator.
      */
     int precedence;
+    /**
+     * The associativity of the operator.
+     */
+    int associativity;
     /**
      * The functionality of the operator.
      */
diff --git a/include/libabacus.h b/include/libabacus.h
index e1fe1a8..728d523 100644
--- a/include/libabacus.h
+++ b/include/libabacus.h
@@ -45,10 +45,11 @@ libab_result libab_init(libab* ab);
  * @param ab the libabacus instance to reigster the operator with.
  * @param op the operator string to register.
  * @param precedence the precedence of the operator.
+ * @param associativity the associativity of the operator.
  * @param func the function that describes the functionality of the operator.
  * @return the result of the initialization.
  */
-libab_result libab_register_operator_infix(libab* ab, const char* op, int precedence, libab_function_ptr func);
+libab_result libab_register_operator_infix(libab* ab, const char* op, int precedence, int associativity, libab_function_ptr func);
 /**
  * Registers an operation with libabacus that appears
  * before its operand.
diff --git a/src/libabacus.c b/src/libabacus.c
index b0dba88..1cd43be 100644
--- a/src/libabacus.c
+++ b/src/libabacus.c
@@ -8,7 +8,7 @@ libab_result libab_init(libab* ab) {
     return libab_lexer_init(&ab->lexer);
 }
 
-libab_result _register_operator(libab* ab, const char* op, int token_type, int precedence, libab_function_ptr func) {
+libab_result _register_operator(libab* ab, const char* op, int token_type, int precedence, int associativity, libab_function_ptr func) {
     libab_result result = LIBAB_SUCCESS;
     libab_table_entry* new_entry;
     if((new_entry = malloc(sizeof(*new_entry)))) {
@@ -35,16 +35,16 @@ libab_result _register_operator(libab* ab, const char* op, int token_type, int p
     return result;
 }
 
-libab_result libab_register_operator_infix(libab* ab, const char* op, int precedence, libab_function_ptr func) {
-    return _register_operator(ab, op, TOKEN_OP_INFIX, precedence, func);
+libab_result libab_register_operator_infix(libab* ab, const char* op, int precedence, int associativity, libab_function_ptr func) {
+    return _register_operator(ab, op, TOKEN_OP_INFIX, precedence, associativity, func);
 }
 
 libab_result libab_register_operator_prefix(libab* ab, const char* op, libab_function_ptr func) {
-    return _register_operator(ab, op, TOKEN_OP_PREFIX, 0, func);
+    return _register_operator(ab, op, TOKEN_OP_PREFIX, 0, 0, func);
 }
 
 libab_result libab_register_operator_postfix(libab* ab, const char* op, libab_function_ptr func) {
-    return _register_operator(ab, op, TOKEN_OP_POSTFIX, 0, func);
+    return _register_operator(ab, op, TOKEN_OP_POSTFIX, 0, 0, func);
 }
 
 libab_result libab_register_function(libab* ab, const char* name, libab_function_ptr func) {