diff --git a/ts/packages/anchor/src/coder/borsh/instruction.ts b/ts/packages/anchor/src/coder/borsh/instruction.ts
index 8b99a0f830..27e31b63e0 100644
--- a/ts/packages/anchor/src/coder/borsh/instruction.ts
+++ b/ts/packages/anchor/src/coder/borsh/instruction.ts
@@ -25,7 +25,7 @@ export class BorshInstructionCoder implements InstructionCoder {
   // Instruction args layout. Maps namespaced method
   private ixLayouts: Map<
     string,
-    { discriminator: IdlDiscriminator; layout: Layout }
+    { discriminator: IdlDiscriminator; layout: Layout; args: IdlField[] }
   >;
 
   public constructor(private idl: Idl) {
@@ -35,7 +35,10 @@ export class BorshInstructionCoder implements InstructionCoder {
         IdlCoder.fieldLayout(arg, idl.types)
       );
       const layout = borsh.struct(fieldLayouts, name);
-      return [name, { discriminator: ix.discriminator, layout }] as const;
+      return [
+        name,
+        { discriminator: ix.discriminator, layout, args: ix.args },
+      ] as const;
     });
     this.ixLayouts = new Map(ixLayouts);
   }
@@ -50,12 +53,186 @@ export class BorshInstructionCoder implements InstructionCoder {
       throw new Error(`Unknown method: ${ixName}`);
     }
 
-    const len = encoder.layout.encode(ix, buffer);
+    const ixWithDefinedOptions = BorshInstructionCoder.convertUndefinedOptions(
+      encoder.args,
+      ix,
+      this.idl.types
+    );
+    const len = encoder.layout.encode(ixWithDefinedOptions, buffer);
     const data = buffer.slice(0, len);
 
     return Buffer.concat([Buffer.from(encoder.discriminator), data]);
   }
 
+  private static convertUndefinedOptions(
+    args: IdlField[],
+    ix: any,
+    types: IdlTypeDef[] = []
+  ): any {
+    const converted = { ...ix };
+    args.forEach((arg) => {
+      converted[arg.name] = BorshInstructionCoder.convertUndefinedOption(
+        arg.type,
+        ix[arg.name],
+        types
+      );
+    });
+    return converted;
+  }
+
+  private static convertUndefinedOption(
+    idlType: IdlType,
+    value: any,
+    types: IdlTypeDef[]
+  ): any {
+    if (typeof idlType === "string") {
+      return value;
+    }
+
+    if ("option" in idlType) {
+      if (value === undefined) {
+        return null;
+      }
+      if (value === null) {
+        return null;
+      }
+      return BorshInstructionCoder.convertUndefinedOption(
+        idlType.option,
+        value,
+        types
+      );
+    }
+
+    if ("vec" in idlType) {
+      return Array.isArray(value)
+        ? value.map((item) =>
+            BorshInstructionCoder.convertUndefinedOption(
+              idlType.vec,
+              item,
+              types
+            )
+          )
+        : value;
+    }
+
+    if ("array" in idlType) {
+      return Array.isArray(value)
+        ? value.map((item) =>
+            BorshInstructionCoder.convertUndefinedOption(
+              idlType.array[0],
+              item,
+              types
+            )
+          )
+        : value;
+    }
+
+    if ("defined" in idlType) {
+      const typeDef = types.find((t) => t.name === idlType.defined.name);
+      if (!typeDef) {
+        return value;
+      }
+      return BorshInstructionCoder.convertUndefinedOptionDefined(
+        typeDef,
+        value,
+        types
+      );
+    }
+
+    return value;
+  }
+
+  private static convertUndefinedOptionDefined(
+    typeDef: IdlTypeDef,
+    value: any,
+    types: IdlTypeDef[]
+  ): any {
+    if (value === null || value === undefined || typeof value !== "object") {
+      return value;
+    }
+
+    switch (typeDef.type.kind) {
+      case "struct": {
+        return handleDefinedFields(
+          typeDef.type.fields,
+          () => value,
+          (fields) => {
+            const converted = { ...value };
+            fields.forEach((field) => {
+              converted[field.name] =
+                BorshInstructionCoder.convertUndefinedOption(
+                  field.type,
+                  value[field.name],
+                  types
+                );
+            });
+            return converted;
+          },
+          (fields) => {
+            const converted = Array.isArray(value) ? [...value] : { ...value };
+            fields.forEach((field, index) => {
+              converted[index] = BorshInstructionCoder.convertUndefinedOption(
+                field,
+                value[index],
+                types
+              );
+            });
+            return converted;
+          }
+        );
+      }
+      case "enum": {
+        const variantName = Object.keys(value)[0];
+        const variant = typeDef.type.variants.find(
+          (v) => v.name === variantName
+        );
+        if (!variant) {
+          return value;
+        }
+
+        return {
+          ...value,
+          [variantName]: handleDefinedFields(
+            variant.fields,
+            () => value[variantName],
+            (fields) => {
+              const converted = { ...value[variantName] };
+              fields.forEach((field) => {
+                converted[field.name] =
+                  BorshInstructionCoder.convertUndefinedOption(
+                    field.type,
+                    value[variantName][field.name],
+                    types
+                  );
+              });
+              return converted;
+            },
+            (fields) => {
+              const converted = Array.isArray(value[variantName])
+                ? [...value[variantName]]
+                : { ...value[variantName] };
+              fields.forEach((field, index) => {
+                converted[index] = BorshInstructionCoder.convertUndefinedOption(
+                  field,
+                  value[variantName][index],
+                  types
+                );
+              });
+              return converted;
+            }
+          ),
+        };
+      }
+      case "type": {
+        return BorshInstructionCoder.convertUndefinedOption(
+          typeDef.type.alias,
+          value,
+          types
+        );
+      }
+    }
+  }
+
   /**
    * Decodes a program instruction.
    */
diff --git a/ts/packages/anchor/tests/coder-instructions.spec.ts b/ts/packages/anchor/tests/coder-instructions.spec.ts
index a87519c3c5..61bd1c28fe 100644
--- a/ts/packages/anchor/tests/coder-instructions.spec.ts
+++ b/ts/packages/anchor/tests/coder-instructions.spec.ts
@@ -1,4 +1,5 @@
 import * as assert from "assert";
+import BN from "bn.js";
 import { BorshCoder } from "../src";
 import { Idl, IdlType } from "../src/idl";
 import { toInstruction } from "../src/program/common";
@@ -53,4 +54,68 @@ describe("coder.instructions", () => {
 
     assert.deepStrictEqual(decoded?.data[idlIx.args[0].name], expected);
   });
+
+  test("Encodes undefined option instruction arguments as null", () => {
+    const idl: Idl = {
+      address: "Test111111111111111111111111111111111111111",
+      metadata: {
+        name: "test",
+        version: "0.0.0",
+        spec: "0.1.0",
+      },
+      instructions: [
+        {
+          name: "initialize",
+          discriminator: [0, 1, 2, 3, 4, 5, 6, 7],
+          accounts: [],
+          args: [
+            {
+              name: "required",
+              type: "bool",
+            },
+            {
+              name: "someArg",
+              type: {
+                option: "u64",
+              },
+            },
+            {
+              name: "someArg2",
+              type: {
+                option: "u64",
+              },
+            },
+          ],
+        },
+      ],
+      types: [],
+    };
+
+    const idlIx = idl.instructions[0];
+    const coder = new BorshCoder(idl);
+    const ix = toInstruction(idlIx, true, undefined, new BN(0x3030));
+
+    const encoded = coder.instruction.encode(idlIx.name, ix);
+    const decoded = coder.instruction.decode(encoded);
+
+    assert.deepStrictEqual(
+      [...encoded],
+      [
+        ...idlIx.discriminator,
+        1, // required bool
+        0, // someArg: None
+        1, // someArg2: Some
+        0x30,
+        0x30,
+        0,
+        0,
+        0,
+        0,
+        0,
+        0,
+      ]
+    );
+    assert.strictEqual(decoded?.data["someArg"], null);
+    assert.ok(decoded?.data["someArg2"].eq(new BN(0x3030)));
+  });
 });