diff --git a/ext/commonmarker/commonmarker.c b/ext/commonmarker/commonmarker.c
index 71509159..111399ed 100644
--- a/ext/commonmarker/commonmarker.c
+++ b/ext/commonmarker/commonmarker.c
@@ -4,7 +4,9 @@
 
 #include "comrak_ffi.h"
 
-int iterate_extension_options(VALUE key, VALUE val, comrak_options_t *config) {
+int iterate_extension_options(VALUE key, VALUE val, VALUE arg) {
+  comrak_options_t *config = (comrak_options_t *)arg;
+
   if (key == ID2SYM(rb_intern("strikethrough"))) {
     if (TYPE(val) == T_TRUE || TYPE(val) == T_FALSE) {
       comrak_set_extension_option_strikethrough(config, val);
@@ -50,7 +52,9 @@ int iterate_extension_options(VALUE key, VALUE val, comrak_options_t *config) {
   return ST_CONTINUE;
 }
 
-int iterate_render_options(VALUE key, VALUE val, comrak_options_t *config) {
+int iterate_render_options(VALUE key, VALUE val, VALUE arg) {
+  comrak_options_t *config = (comrak_options_t *)arg;
+
   if (key == ID2SYM(rb_intern("hardbreaks"))) {
     if (TYPE(val) == T_TRUE || TYPE(val) == T_FALSE) {
       comrak_set_render_option_hardbreaks(config, val);
@@ -77,7 +81,9 @@ int iterate_render_options(VALUE key, VALUE val, comrak_options_t *config) {
   return ST_CONTINUE;
 }
 
-int iterate_parse_options(VALUE key, VALUE val, comrak_options_t *config) {
+int iterate_parse_options(VALUE key, VALUE val, VALUE arg) {
+  comrak_options_t *config = (comrak_options_t *)arg;
+
   if (key == ID2SYM(rb_intern("smart"))) {
     if (TYPE(val) == T_TRUE || TYPE(val) == T_FALSE) {
       comrak_set_parse_option_smart(config, val);
@@ -92,22 +98,24 @@ int iterate_parse_options(VALUE key, VALUE val, comrak_options_t *config) {
   return ST_CONTINUE;
 }
 
-int iterate_options_hash(VALUE rb_option_key, VALUE rb_option_val, comrak_options_t *config) {
+int iterate_options_hash(VALUE rb_option_key, VALUE rb_option_val, VALUE arg) {
+  comrak_options_t *config = (comrak_options_t *)arg;
+
   Check_Type(rb_option_key, T_SYMBOL);
 
   // which options are we dealing with?
   if (rb_option_key == ID2SYM(rb_intern("parse"))) {
     Check_Type(rb_option_val, T_HASH);
-    rb_hash_foreach(rb_option_val, iterate_parse_options, config);
+    rb_hash_foreach(rb_option_val, iterate_parse_options, (VALUE)config);
   } else if (rb_option_key == ID2SYM(rb_intern("render"))) {
     Check_Type(rb_option_val, T_HASH);
-    rb_hash_foreach(rb_option_val, iterate_render_options, config);
+    rb_hash_foreach(rb_option_val, iterate_render_options, (VALUE)config);
   } else if (rb_option_key == ID2SYM(rb_intern("extension"))) {
     Check_Type(rb_option_val, T_HASH);
     if (rb_hash_aref(rb_option_val, ID2SYM(rb_intern("header_ids"))) == Qnil) {
       comrak_set_extension_option_header_ids(config, NULL, 0);
     }
-    rb_hash_foreach(rb_option_val, iterate_extension_options, config);
+    rb_hash_foreach(rb_option_val, iterate_extension_options, (VALUE)config);
 
   }
 
@@ -121,7 +129,7 @@ VALUE commonmark_to_html(VALUE self, VALUE rb_commonmark, VALUE rb_options) {
   char *commonmark = StringValueCStr(rb_commonmark);
 
   comrak_options_t *options = comrak_options_new();
-  rb_hash_foreach(rb_options, iterate_options_hash, options);
+  rb_hash_foreach(rb_options, iterate_options_hash, (VALUE)options);
 
   comrak_str_t html = comrak_commonmark_to_html(commonmark, options);