diff --git a/ext/openssl/ossl_bn.c b/ext/openssl/ossl_bn.c
index 7eb1bc79a5..06647b5b62 100644
--- a/ext/openssl/ossl_bn.c
+++ b/ext/openssl/ossl_bn.c
@@ -591,6 +591,13 @@ BIGNUM_2c(mod_sqr)
 	return obj;						\
     }
 
+/*
+ * Document-method: OpenSSL::BN#mod_sqrt
+ * call-seq:
+ *   bn.mod_sqrt(bn2) => aBN
+ */
+BIGNUM_2cr(mod_sqrt)
+
 /*
  * call-seq:
  *    bn.mod_inverse(bn2) => aBN
@@ -1237,6 +1244,7 @@ Init_ossl_bn(void)
     rb_define_method(cBN, "mod_sub", ossl_bn_mod_sub, 2);
     rb_define_method(cBN, "mod_mul", ossl_bn_mod_mul, 2);
     rb_define_method(cBN, "mod_sqr", ossl_bn_mod_sqr, 1);
+    rb_define_method(cBN, "mod_sqrt", ossl_bn_mod_sqrt, 1);
     rb_define_method(cBN, "**", ossl_bn_exp, 1);
     rb_define_method(cBN, "mod_exp", ossl_bn_mod_exp, 2);
     rb_define_method(cBN, "gcd", ossl_bn_gcd, 1);
diff --git a/test/openssl/test_bn.rb b/test/openssl/test_bn.rb
index 346602dada..77af14091e 100644
--- a/test/openssl/test_bn.rb
+++ b/test/openssl/test_bn.rb
@@ -174,6 +174,12 @@ class OpenSSL::TestBN < OpenSSL::TestCase
     assert_equal(0, 59.to_bn.mod_sqr(59))
   end
 
+  def test_mod_sqrt
+    assert_equal(3, 4.to_bn.mod_sqrt(5))
+    assert_equal(0, 5.to_bn.mod_sqrt(5))
+    assert_raise(OpenSSL::BNError) { 3.to_bn.mod_sqrt(5) }
+  end
+
   def test_mod_inverse
     assert_equal(2, 3.to_bn.mod_inverse(5))
     assert_raise(OpenSSL::BNError) { 3.to_bn.mod_inverse(6) }