diff --git a/docs/index.md b/docs/index.md
index 8e625d3b..b0952b4c 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -284,8 +284,8 @@ Name | Type | Description
 ---- | ---- | -----------
 fee | [value](#value) | *Optional* An exact fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
 maxFee | [value](#value) | *Optional* The maximum fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
-maxLedgerVersion | integer | *Optional* The highest ledger version that the transaction can be included in.
-maxLedgerVersionOffset | integer | *Optional* Offset from current legder version to highest ledger version that the transaction can be included in.
+maxLedgerVersion | integer,null | *Optional* The highest ledger version that the transaction can be included in. If this option and `maxLedgerVersionOffset` are both omitted, the `maxLedgerVersion` option will default to 3 greater than the current validated ledger version (equivalent to `maxLedgerVersionOffset=3`). Use `null` to not set a maximum ledger version.
+maxLedgerVersionOffset | integer | *Optional* Offset from current validated legder version to highest ledger version that the transaction can be included in.
 sequence | [sequence](#account-sequence-number) | *Optional* The initiating account's sequence number for this transaction.
 
 We recommended that you specify a `maxLedgerVersion` so that you can quickly determine that a failed transaction will never succeeed in the future. It is impossible for a transaction to succeed after the network ledger version exceeds the transaction's `maxLedgerVersion`. If you omit `maxLedgerVersion`, the "prepare*" method automatically supplies a `maxLedgerVersion` equal to the current ledger plus 3, which it includes in the return value from the "prepare*" method.
@@ -2800,7 +2800,7 @@ txJSON | string | The prepared transaction in rippled JSON format.
 instructions | object | The instructions for how to execute the transaction after adding automatic defaults.
 *instructions.* fee | [value](#value) | An exact fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
 *instructions.* sequence | [sequence](#account-sequence-number) | The initiating account's sequence number for this transaction.
-*instructions.* maxLedgerVersion | integer | *Optional* The highest ledger version that the transaction can be included in.
+*instructions.* maxLedgerVersion | integer,null | The highest ledger version that the transaction can be included in. Set to `null` if there is no maximum.
 
 ### Example
 
@@ -2869,7 +2869,7 @@ txJSON | string | The prepared transaction in rippled JSON format.
 instructions | object | The instructions for how to execute the transaction after adding automatic defaults.
 *instructions.* fee | [value](#value) | An exact fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
 *instructions.* sequence | [sequence](#account-sequence-number) | The initiating account's sequence number for this transaction.
-*instructions.* maxLedgerVersion | integer | *Optional* The highest ledger version that the transaction can be included in.
+*instructions.* maxLedgerVersion | integer,null | The highest ledger version that the transaction can be included in. Set to `null` if there is no maximum.
 
 ### Example
 
@@ -2936,7 +2936,7 @@ txJSON | string | The prepared transaction in rippled JSON format.
 instructions | object | The instructions for how to execute the transaction after adding automatic defaults.
 *instructions.* fee | [value](#value) | An exact fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
 *instructions.* sequence | [sequence](#account-sequence-number) | The initiating account's sequence number for this transaction.
-*instructions.* maxLedgerVersion | integer | *Optional* The highest ledger version that the transaction can be included in.
+*instructions.* maxLedgerVersion | integer,null | The highest ledger version that the transaction can be included in. Set to `null` if there is no maximum.
 
 ### Example
 
@@ -3001,7 +3001,7 @@ txJSON | string | The prepared transaction in rippled JSON format.
 instructions | object | The instructions for how to execute the transaction after adding automatic defaults.
 *instructions.* fee | [value](#value) | An exact fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
 *instructions.* sequence | [sequence](#account-sequence-number) | The initiating account's sequence number for this transaction.
-*instructions.* maxLedgerVersion | integer | *Optional* The highest ledger version that the transaction can be included in.
+*instructions.* maxLedgerVersion | integer,null | The highest ledger version that the transaction can be included in. Set to `null` if there is no maximum.
 
 ### Example
 
@@ -3053,7 +3053,7 @@ txJSON | string | The prepared transaction in rippled JSON format.
 instructions | object | The instructions for how to execute the transaction after adding automatic defaults.
 *instructions.* fee | [value](#value) | An exact fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
 *instructions.* sequence | [sequence](#account-sequence-number) | The initiating account's sequence number for this transaction.
-*instructions.* maxLedgerVersion | integer | *Optional* The highest ledger version that the transaction can be included in.
+*instructions.* maxLedgerVersion | integer,null | The highest ledger version that the transaction can be included in. Set to `null` if there is no maximum.
 
 ### Example
 
@@ -3118,7 +3118,7 @@ txJSON | string | The prepared transaction in rippled JSON format.
 instructions | object | The instructions for how to execute the transaction after adding automatic defaults.
 *instructions.* fee | [value](#value) | An exact fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
 *instructions.* sequence | [sequence](#account-sequence-number) | The initiating account's sequence number for this transaction.
-*instructions.* maxLedgerVersion | integer | *Optional* The highest ledger version that the transaction can be included in.
+*instructions.* maxLedgerVersion | integer,null | The highest ledger version that the transaction can be included in. Set to `null` if there is no maximum.
 
 ### Example
 
@@ -3190,7 +3190,7 @@ txJSON | string | The prepared transaction in rippled JSON format.
 instructions | object | The instructions for how to execute the transaction after adding automatic defaults.
 *instructions.* fee | [value](#value) | An exact fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
 *instructions.* sequence | [sequence](#account-sequence-number) | The initiating account's sequence number for this transaction.
-*instructions.* maxLedgerVersion | integer | *Optional* The highest ledger version that the transaction can be included in.
+*instructions.* maxLedgerVersion | integer,null | The highest ledger version that the transaction can be included in. Set to `null` if there is no maximum.
 
 ### Example
 
@@ -3247,7 +3247,7 @@ txJSON | string | The prepared transaction in rippled JSON format.
 instructions | object | The instructions for how to execute the transaction after adding automatic defaults.
 *instructions.* fee | [value](#value) | An exact fee to pay for the transaction. See [Transaction Fees](#transaction-fees) for more information.
 *instructions.* sequence | [sequence](#account-sequence-number) | The initiating account's sequence number for this transaction.
-*instructions.* maxLedgerVersion | integer | *Optional* The highest ledger version that the transaction can be included in.
+*instructions.* maxLedgerVersion | integer,null | The highest ledger version that the transaction can be included in. Set to `null` if there is no maximum.
 
 ### Example
 
diff --git a/src/common/schemas/objects/instructions.json b/src/common/schemas/objects/instructions.json
index 38d68ff9..a267e0f7 100644
--- a/src/common/schemas/objects/instructions.json
+++ b/src/common/schemas/objects/instructions.json
@@ -18,11 +18,14 @@
       "$ref": "value"
     },
     "maxLedgerVersion": {
-      "description": "The highest ledger version that the transaction can be included in.",
-      "$ref": "ledgerVersion"
+      "description": "The highest ledger version that the transaction can be included in. If this option and `maxLedgerVersionOffset` are both omitted, the `maxLedgerVersion` option will default to 3 greater than the current validated ledger version (equivalent to `maxLedgerVersionOffset=3`). Use `null` to not set a maximum ledger version.",
+      "oneOf": [
+        {"$ref": "ledgerVersion"},
+        {"type": "null"}
+      ]
     },
     "maxLedgerVersionOffset": {
-      "description": "Offset from current legder version to highest ledger version that the transaction can be included in.",
+      "description": "Offset from current validated legder version to highest ledger version that the transaction can be included in.",
       "type": "integer",
       "minimum": 0
     }
diff --git a/src/common/schemas/output/prepare.json b/src/common/schemas/output/prepare.json
index 0ceff494..73340463 100644
--- a/src/common/schemas/output/prepare.json
+++ b/src/common/schemas/output/prepare.json
@@ -21,12 +21,15 @@
           "description": "The initiating account's sequence number for this transaction."
         },
         "maxLedgerVersion": {
-          "$ref": "ledgerVersion",
-          "description": "The highest ledger version that the transaction can be included in."
+          "oneOf": [
+            {"$ref": "ledgerVersion"},
+            {"type": "null"}
+          ],
+          "description": "The highest ledger version that the transaction can be included in. Set to `null` if there is no maximum."
         }
       },
       "additionalProperties": false,
-      "required": ["fee", "sequence"]
+      "required": ["fee", "sequence", "maxLedgerVersion"]
     }
   },
   "additionalProperties": false,
diff --git a/src/transaction/utils.js b/src/transaction/utils.js
index a5b33463..532e67d9 100644
--- a/src/transaction/utils.js
+++ b/src/transaction/utils.js
@@ -10,7 +10,8 @@ function formatPrepareResponse(txJSON: Object): Object {
   const instructions = {
     fee: common.dropsToXrp(txJSON.Fee),
     sequence: txJSON.Sequence,
-    maxLedgerVersion: txJSON.LastLedgerSequence
+    maxLedgerVersion: txJSON.LastLedgerSequence === undefined ?
+      null : txJSON.LastLedgerSequence
   };
   return {
     txJSON: JSON.stringify(txJSON),
@@ -36,7 +37,9 @@ function prepareTransaction(txJSON: Object, api: Object,
 
   function prepareMaxLedgerVersion(): Promise<Object> {
     if (instructions.maxLedgerVersion !== undefined) {
-      txJSON.LastLedgerSequence = instructions.maxLedgerVersion;
+      if (instructions.maxLedgerVersion !== null) {
+        txJSON.LastLedgerSequence = instructions.maxLedgerVersion;
+      }
       return Promise.resolve(txJSON);
     }
     const offset = instructions.maxLedgerVersionOffset !== undefined ?
diff --git a/test/api-test.js b/test/api-test.js
index da00be84..79fddb1a 100644
--- a/test/api-test.js
+++ b/test/api-test.js
@@ -186,6 +186,13 @@ describe('RippleAPI', function() {
       _.partial(checkResult, responses.prepareSettings.flags, 'prepare'));
   });
 
+  it('prepareSettings - no maxLedgerVersion', function() {
+    return this.api.prepareSettings(
+      address, requests.prepareSettings, {maxLedgerVersion: null}).then(
+      _.partial(checkResult, responses.prepareSettings.noMaxLedgerVersion,
+        'prepare'));
+  });
+
   it('prepareSettings - no instructions', function() {
     return this.api.prepareSettings(
       address, requests.prepareSettings).then(
diff --git a/test/fixtures/responses/index.js b/test/fixtures/responses/index.js
index 967bbfd5..d9004049 100644
--- a/test/fixtures/responses/index.js
+++ b/test/fixtures/responses/index.js
@@ -86,7 +86,8 @@ module.exports = {
     setTransferRate: require('./prepare-settings-set-transfer-rate.json'),
     fieldClear: require('./prepare-settings-field-clear.json'),
     noInstructions: require('./prepare-settings-no-instructions.json'),
-    signed: require('./prepare-settings-signed.json')
+    signed: require('./prepare-settings-signed.json'),
+    noMaxLedgerVersion: require('./prepare-settings-no-maxledgerversion.json')
   },
   prepareSuspendedPaymentCreation: {
     normal: require('./prepare-suspended-payment-creation'),
diff --git a/test/fixtures/responses/prepare-settings-no-maxledgerversion.json b/test/fixtures/responses/prepare-settings-no-maxledgerversion.json
new file mode 100644
index 00000000..9e207bc3
--- /dev/null
+++ b/test/fixtures/responses/prepare-settings-no-maxledgerversion.json
@@ -0,0 +1,8 @@
+{
+  "txJSON": "{\"TransactionType\":\"AccountSet\",\"Account\":\"r9cZA1mLK5R5Am25ArfXFmqgNwjZgnfk59\",\"Memos\":[{\"Memo\":{\"MemoData\":\"7465787465642064617461\",\"MemoType\":\"74657374\",\"MemoFormat\":\"706C61696E2F74657874\"}}],\"Domain\":\"726970706C652E636F6D\",\"Flags\":2147483648,\"Fee\":\"12\",\"Sequence\":23}",
+  "instructions": {
+    "fee": "0.000012",
+    "sequence": 23,
+    "maxLedgerVersion": null
+  }
+}