Index: ossl_cipher.c
===================================================================
--- ossl_cipher.c	(revision 42064)
+++ ossl_cipher.c	(working copy)
@@ -677,6 +677,27 @@
     return key_length;
 }
 
+/*
+ *  call-seq:
+ *     cipher.iv_len = integer -> integer
+ *
+ *  Sets the iv length of the cipher.
+ *
+ *  See EVP_CTRL_GCM_SET_IVLEN for further information.
+ */
+static VALUE
+ossl_cipher_set_gcm_iv_length(VALUE self, VALUE iv_length)
+{
+    int ivlen = NUM2INT(iv_length);
+    EVP_CIPHER_CTX *ctx;
+
+    GetCipher(self, ctx);
+    if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, ivlen, NULL) != 1)
+        ossl_raise(eCipherError, NULL);
+
+    return iv_length;
+}
+
 #if defined(HAVE_EVP_CIPHER_CTX_SET_PADDING)
 /*
  *  call-seq:
@@ -963,6 +984,7 @@
     rb_define_method(cCipher, "key_len=", ossl_cipher_set_key_length, 1);
     rb_define_method(cCipher, "key_len", ossl_cipher_key_length, 0);
     rb_define_method(cCipher, "iv=", ossl_cipher_set_iv, 1);
+    rb_define_method(cCipher, "iv_len=", ossl_cipher_set_gcm_iv_length, 1);
     rb_define_method(cCipher, "iv_len", ossl_cipher_iv_length, 0);
     rb_define_method(cCipher, "block_size", ossl_cipher_block_size, 0);
     rb_define_method(cCipher, "padding=", ossl_cipher_set_padding, 1);