diff --git a/ext/openssl/ossl.h b/ext/openssl/ossl.h
index 7762ad237..d16be868f 100644
--- a/ext/openssl/ossl.h
+++ b/ext/openssl/ossl.h
@@ -102,11 +102,27 @@ void ossl_want_uninitialized(VALUE self, const rb_data_type_t *type);
  */
 #ifndef HAVE_RB_LEN_T /* Ruby 4.1 */
 typedef long rb_len_t;
+typedef unsigned long rb_ulen_t;
+#endif
+#ifndef SIZEOF_RB_LEN_T
 # define SIZEOF_RB_LEN_T SIZEOF_LONG
+#endif
+#ifndef RB_LEN_MAX
 # define RB_LEN_MAX LONG_MAX
+#endif
+#ifndef PRIdLEN
 # define PRIdLEN "ld"
+#endif
+#ifndef FIX2LEN
+# define FIX2LEN FIX2LONG
+#endif
+#ifndef NUM2LEN
 # define NUM2LEN NUM2LONG
+#endif
+#ifndef LEN2NUM
 # define LEN2NUM LONG2NUM
+#endif
+#ifndef HAVE_RB_LEN_T
 static inline long
 rb_len2long(rb_len_t n)
 {
diff --git a/ext/openssl/ossl_bn.c b/ext/openssl/ossl_bn.c
index ff5d3a538..56d7e00d2 100644
--- a/ext/openssl/ossl_bn.c
+++ b/ext/openssl/ossl_bn.c
@@ -75,12 +75,12 @@ integer_to_bnptr(VALUE obj, BIGNUM *orig)
     BIGNUM *bn;
 
     if (FIXNUM_P(obj)) {
-        long i;
-        unsigned char bin[sizeof(long)];
-        long n = FIX2LONG(obj);
-        unsigned long un = labs(n);
+        size_t i;
+        unsigned char bin[sizeof(rb_ulen_t)];
+        rb_len_t n = FIX2LEN(obj);
+        rb_ulen_t un = n < 0 ? 0 - (rb_ulen_t)n : (rb_ulen_t)n;
 
-        for (i = sizeof(long) - 1; 0 <= i; i--) {
+        for (i = sizeof(bin); 0 < i--;) {
             bin[i] = un & 0xff;
             un >>= 8;
         }