diff --git a/ext/psych/psych.h b/ext/psych/psych.h
index 0e146588..3548ece3 100644
--- a/ext/psych/psych.h
+++ b/ext/psych/psych.h
@@ -4,6 +4,10 @@
 #include <ruby.h>
 #include <ruby/encoding.h>
 
+#ifndef HAVE_RB_LEN_T
+typedef long rb_len_t;
+#endif
+
 #ifdef PSYCH_USE_LIBFYAML
 #include <libfyaml.h>
 #else
diff --git a/ext/psych/psych_emitter.c b/ext/psych/psych_emitter.c
index 187aebc3..afe273d6 100644
--- a/ext/psych/psych_emitter.c
+++ b/ext/psych/psych_emitter.c
@@ -25,7 +25,7 @@ static void emit(yaml_emitter_t * emitter, yaml_event_t * event)
 static int writer(void *ctx, unsigned char *buffer, size_t size)
 {
     VALUE self = (VALUE)ctx, io = rb_attr_get(self, id_io);
-    VALUE str = rb_enc_str_new((const char *)buffer, (long)size, rb_utf8_encoding());
+    VALUE str = rb_enc_str_new((const char *)buffer, (rb_len_t)size, rb_utf8_encoding());
     VALUE wrote = rb_funcall(io, id_write, 1, str);
     return (int)NUM2INT(wrote);
 }
@@ -172,8 +172,8 @@ static VALUE start_document_try(VALUE d)
     }
 
     if(RTEST(tags)) {
-        long i = 0;
-        long len;
+        rb_len_t i = 0;
+        rb_len_t len;
         rb_encoding * encoding = rb_utf8_encoding();
 
         Check_Type(tags, T_ARRAY);
diff --git a/ext/psych/psych_emitter_fy.c b/ext/psych/psych_emitter_fy.c
index 22bf23e5..4834d9f7 100644
--- a/ext/psych/psych_emitter_fy.c
+++ b/ext/psych/psych_emitter_fy.c
@@ -33,7 +33,7 @@ static int emitter_output(struct fy_emitter *emit, enum fy_emitter_write_type ty
 {
     VALUE self = (VALUE)userdata;
     VALUE io = rb_attr_get(self, id_io);
-    VALUE s = rb_enc_str_new(str, (long)len, rb_utf8_encoding());
+    VALUE s = rb_enc_str_new(str, (rb_len_t)len, rb_utf8_encoding());
     rb_funcall(io, id_write, 1, s);
     return len;
 }
@@ -186,7 +186,7 @@ static VALUE start_document_try(VALUE d)
 
     if (RTEST(tags)) {
         rb_encoding *encoding = rb_utf8_encoding();
-        long i, len;
+        rb_len_t i, len;
         Check_Type(tags, T_ARRAY);
         len = RARRAY_LEN(tags);
         if (len > 0) {
diff --git a/ext/psych/psych_parser.c b/ext/psych/psych_parser.c
index 2b50fcae..bb37623f 100644
--- a/ext/psych/psych_parser.c
+++ b/ext/psych/psych_parser.c
@@ -419,7 +419,7 @@ static VALUE parse_body(VALUE ptr)
                 VALUE plain_implicit, quoted_implicit, style;
                 VALUE val = rb_str_new(
                     (const char *)event.data.scalar.value,
-                    (long)event.data.scalar.length
+                    (rb_len_t)event.data.scalar.length
                     );
 
                 PSYCH_TRANSCODE(val, encoding, internal_enc);
diff --git a/ext/psych/psych_parser_fy.c b/ext/psych/psych_parser_fy.c
index ccb05776..e79ec360 100644
--- a/ext/psych/psych_parser_fy.c
+++ b/ext/psych/psych_parser_fy.c
@@ -256,7 +256,7 @@ static VALUE token_to_str(struct fy_token *tok, int encoding, rb_encoding *inter
     if (!text) {
         return Qnil;
     }
-    VALUE str = rb_str_new(text, (long)len);
+    VALUE str = rb_str_new(text, (rb_len_t)len);
     PSYCH_TRANSCODE(str, encoding, internal_enc);
     return str;
 }