diff --git a/action.yml b/action.yml
index 2ed0d92..b76193a 100644
--- a/action.yml
+++ b/action.yml
@@ -12,7 +12,7 @@ inputs:
   commit-msg:
     description: "The message provided with the commit"
     required: false
-    default: "flake.lock: Update"
+    default: ""
   base:
     description: "Sets the pull request base branch. Defaults to the branch checked out in the workflow."
     required: false
diff --git a/dist/index.js b/dist/index.js
index 4ac9a72..c8bc043 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -95326,11 +95326,7 @@ function makeNixCommandArgs(nixOptions, flakeInputs, commitMessage) {
     "--update-input",
     input
   ]);
-  const lockfileSummaryFlags = [
-    "--option",
-    "commit-lockfile-summary",
-    commitMessage
-  ];
+  const lockfileSummaryFlags = commitMessage ? ["--option", "commit-lockfile-summary", commitMessage] : [];
   const updateLockMechanism = flakeInputFlags.length === 0 ? "update" : "lock";
   return nixOptions.concat(["flake", updateLockMechanism]).concat(flakeInputFlags).concat(["--commit-lock-file"]).concat(lockfileSummaryFlags);
 }
diff --git a/dist/index.js.map b/dist/index.js.map
index 2e2062e..d19c49c 100644
--- a/dist/index.js.map
+++ b/dist/index.js.map
@@ -1 +1 @@
-{"version":3,"sources":["../src/nix.ts","../src/index.ts"],"sourcesContent":["// Build the Nix args out of inputs from the Actions environment\nexport function makeNixCommandArgs(\n  nixOptions: string[],\n  flakeInputs: string[],\n  commitMessage: string,\n): string[] {\n  const flakeInputFlags = flakeInputs.flatMap((input) => [\n    \"--update-input\",\n    input,\n  ]);\n\n  // NOTE(cole-h): In Nix versions 2.23.0 and later, `commit-lockfile-summary` became an alias to\n  // the setting `commit-lock-file-summary` (https://github.com/NixOS/nix/pull/10691), and Nix does\n  // not treat aliases the same as their \"real\" setting by requiring setting aliases to be\n  // configured via `--option <alias name> <option value>`\n  // (https://github.com/NixOS/nix/issues/10989).\n  // So, we go the long way so that we can support versions both before and after Nix 2.23.0.\n  const lockfileSummaryFlags = [\n    \"--option\",\n    \"commit-lockfile-summary\",\n    commitMessage,\n  ];\n\n  const updateLockMechanism = flakeInputFlags.length === 0 ? \"update\" : \"lock\";\n\n  return nixOptions\n    .concat([\"flake\", updateLockMechanism])\n    .concat(flakeInputFlags)\n    .concat([\"--commit-lock-file\"])\n    .concat(lockfileSummaryFlags);\n}\n","import { makeNixCommandArgs } from \"./nix.js\";\nimport * as actionsCore from \"@actions/core\";\nimport * as actionsExec from \"@actions/exec\";\nimport { DetSysAction, inputs } from \"detsys-ts\";\n\nconst EVENT_EXECUTION_FAILURE = \"execution_failure\";\n\nclass UpdateFlakeLockAction extends DetSysAction {\n  private commitMessage: string;\n  private nixOptions: string[];\n  private flakeInputs: string[];\n  private pathToFlakeDir: string | null;\n\n  constructor() {\n    super({\n      name: \"update-flake-lock\",\n      fetchStyle: \"universal\",\n      requireNix: \"fail\",\n    });\n\n    this.commitMessage = inputs.getString(\"commit-msg\");\n    this.flakeInputs = inputs.getArrayOfStrings(\"inputs\", \"space\");\n    this.nixOptions = inputs.getArrayOfStrings(\"nix-options\", \"space\");\n    this.pathToFlakeDir = inputs.getStringOrNull(\"path-to-flake-dir\");\n  }\n\n  async main(): Promise<void> {\n    await this.update();\n  }\n\n  // No post phase\n  async post(): Promise<void> {}\n\n  async update(): Promise<void> {\n    // Nix command of this form:\n    // nix ${maybe nix options} flake ${\"update\" or \"lock\"} ${maybe --update-input flags} --commit-lock-file --commit-lockfile-summary ${commit message}\n    // Example commands:\n    // nix --extra-substituters https://example.com flake lock --update-input nixpkgs --commit-lock-file --commit-lockfile-summary \"updated flake.lock\"\n    // nix flake update --commit-lock-file --commit-lockfile-summary \"updated flake.lock\"\n    const nixCommandArgs: string[] = makeNixCommandArgs(\n      this.nixOptions,\n      this.flakeInputs,\n      this.commitMessage,\n    );\n\n    actionsCore.debug(\n      JSON.stringify({\n        options: this.nixOptions,\n        inputs: this.flakeInputs,\n        message: this.commitMessage,\n        args: nixCommandArgs,\n      }),\n    );\n\n    const execOptions: actionsExec.ExecOptions = {\n      cwd: this.pathToFlakeDir !== null ? this.pathToFlakeDir : undefined,\n      ignoreReturnCode: true,\n    };\n\n    const exitCode = await actionsExec.exec(\"nix\", nixCommandArgs, execOptions);\n\n    if (exitCode !== 0) {\n      this.recordEvent(EVENT_EXECUTION_FAILURE, {\n        exitCode,\n      });\n      actionsCore.setFailed(`non-zero exit code of ${exitCode} detected`);\n    } else {\n      actionsCore.info(`flake.lock file was successfully updated`);\n    }\n  }\n}\n\nfunction main(): void {\n  new UpdateFlakeLockAction().execute();\n}\n\nmain();\n"],"mappings":";AACO,SAAS,mBACd,YACA,aACA,eACU;AACV,QAAM,kBAAkB,YAAY,QAAQ,CAAC,UAAU;AAAA,IACrD;AAAA,IACA;AAAA,EACF,CAAC;AAQD,QAAM,uBAAuB;AAAA,IAC3B;AAAA,IACA;AAAA,IACA;AAAA,EACF;AAEA,QAAM,sBAAsB,gBAAgB,WAAW,IAAI,WAAW;AAEtE,SAAO,WACJ,OAAO,CAAC,SAAS,mBAAmB,CAAC,EACrC,OAAO,eAAe,EACtB,OAAO,CAAC,oBAAoB,CAAC,EAC7B,OAAO,oBAAoB;AAChC;;;AC7BA,YAAY,iBAAiB;AAC7B,YAAY,iBAAiB;AAC7B,SAAS,cAAc,cAAc;AAErC,IAAM,0BAA0B;AAEhC,IAAM,wBAAN,cAAoC,aAAa;AAAA,EAM/C,cAAc;AACZ,UAAM;AAAA,MACJ,MAAM;AAAA,MACN,YAAY;AAAA,MACZ,YAAY;AAAA,IACd,CAAC;AAED,SAAK,gBAAgB,OAAO,UAAU,YAAY;AAClD,SAAK,cAAc,OAAO,kBAAkB,UAAU,OAAO;AAC7D,SAAK,aAAa,OAAO,kBAAkB,eAAe,OAAO;AACjE,SAAK,iBAAiB,OAAO,gBAAgB,mBAAmB;AAAA,EAClE;AAAA,EAEA,MAAM,OAAsB;AAC1B,UAAM,KAAK,OAAO;AAAA,EACpB;AAAA;AAAA,EAGA,MAAM,OAAsB;AAAA,EAAC;AAAA,EAE7B,MAAM,SAAwB;AAM5B,UAAM,iBAA2B;AAAA,MAC/B,KAAK;AAAA,MACL,KAAK;AAAA,MACL,KAAK;AAAA,IACP;AAEA,IAAY;AAAA,MACV,KAAK,UAAU;AAAA,QACb,SAAS,KAAK;AAAA,QACd,QAAQ,KAAK;AAAA,QACb,SAAS,KAAK;AAAA,QACd,MAAM;AAAA,MACR,CAAC;AAAA,IACH;AAEA,UAAM,cAAuC;AAAA,MAC3C,KAAK,KAAK,mBAAmB,OAAO,KAAK,iBAAiB;AAAA,MAC1D,kBAAkB;AAAA,IACpB;AAEA,UAAM,WAAW,MAAkB,iBAAK,OAAO,gBAAgB,WAAW;AAE1E,QAAI,aAAa,GAAG;AAClB,WAAK,YAAY,yBAAyB;AAAA,QACxC;AAAA,MACF,CAAC;AACD,MAAY,sBAAU,yBAAyB,QAAQ,WAAW;AAAA,IACpE,OAAO;AACL,MAAY,iBAAK,0CAA0C;AAAA,IAC7D;AAAA,EACF;AACF;AAEA,SAAS,OAAa;AACpB,MAAI,sBAAsB,EAAE,QAAQ;AACtC;AAEA,KAAK;","names":[]}
\ No newline at end of file
+{"version":3,"sources":["../src/nix.ts","../src/index.ts"],"sourcesContent":["// Build the Nix args out of inputs from the Actions environment\nexport function makeNixCommandArgs(\n  nixOptions: string[],\n  flakeInputs: string[],\n  commitMessage: string,\n): string[] {\n  const flakeInputFlags = flakeInputs.flatMap((input) => [\n    \"--update-input\",\n    input,\n  ]);\n\n  // NOTE(cole-h): In Nix versions 2.23.0 and later, `commit-lockfile-summary` became an alias to\n  // the setting `commit-lock-file-summary` (https://github.com/NixOS/nix/pull/10691), and Nix does\n  // not treat aliases the same as their \"real\" setting by requiring setting aliases to be\n  // configured via `--option <alias name> <option value>`\n  // (https://github.com/NixOS/nix/issues/10989).\n  // So, we go the long way so that we can support versions both before and after Nix 2.23.0.\n  const lockfileSummaryFlags = commitMessage\n    ? [\"--option\", \"commit-lockfile-summary\", commitMessage]\n    : [];\n\n  const updateLockMechanism = flakeInputFlags.length === 0 ? \"update\" : \"lock\";\n\n  return nixOptions\n    .concat([\"flake\", updateLockMechanism])\n    .concat(flakeInputFlags)\n    .concat([\"--commit-lock-file\"])\n    .concat(lockfileSummaryFlags);\n}\n","import { makeNixCommandArgs } from \"./nix.js\";\nimport * as actionsCore from \"@actions/core\";\nimport * as actionsExec from \"@actions/exec\";\nimport { DetSysAction, inputs } from \"detsys-ts\";\n\nconst EVENT_EXECUTION_FAILURE = \"execution_failure\";\n\nclass UpdateFlakeLockAction extends DetSysAction {\n  private commitMessage: string;\n  private nixOptions: string[];\n  private flakeInputs: string[];\n  private pathToFlakeDir: string | null;\n\n  constructor() {\n    super({\n      name: \"update-flake-lock\",\n      fetchStyle: \"universal\",\n      requireNix: \"fail\",\n    });\n\n    this.commitMessage = inputs.getString(\"commit-msg\");\n    this.flakeInputs = inputs.getArrayOfStrings(\"inputs\", \"space\");\n    this.nixOptions = inputs.getArrayOfStrings(\"nix-options\", \"space\");\n    this.pathToFlakeDir = inputs.getStringOrNull(\"path-to-flake-dir\");\n  }\n\n  async main(): Promise<void> {\n    await this.update();\n  }\n\n  // No post phase\n  async post(): Promise<void> {}\n\n  async update(): Promise<void> {\n    // Nix command of this form:\n    // nix ${maybe nix options} flake ${\"update\" or \"lock\"} ${maybe --update-input flags} --commit-lock-file --commit-lockfile-summary ${commit message}\n    // Example commands:\n    // nix --extra-substituters https://example.com flake lock --update-input nixpkgs --commit-lock-file --commit-lockfile-summary \"updated flake.lock\"\n    // nix flake update --commit-lock-file --commit-lockfile-summary \"updated flake.lock\"\n    const nixCommandArgs: string[] = makeNixCommandArgs(\n      this.nixOptions,\n      this.flakeInputs,\n      this.commitMessage,\n    );\n\n    actionsCore.debug(\n      JSON.stringify({\n        options: this.nixOptions,\n        inputs: this.flakeInputs,\n        message: this.commitMessage,\n        args: nixCommandArgs,\n      }),\n    );\n\n    const execOptions: actionsExec.ExecOptions = {\n      cwd: this.pathToFlakeDir !== null ? this.pathToFlakeDir : undefined,\n      ignoreReturnCode: true,\n    };\n\n    const exitCode = await actionsExec.exec(\"nix\", nixCommandArgs, execOptions);\n\n    if (exitCode !== 0) {\n      this.recordEvent(EVENT_EXECUTION_FAILURE, {\n        exitCode,\n      });\n      actionsCore.setFailed(`non-zero exit code of ${exitCode} detected`);\n    } else {\n      actionsCore.info(`flake.lock file was successfully updated`);\n    }\n  }\n}\n\nfunction main(): void {\n  new UpdateFlakeLockAction().execute();\n}\n\nmain();\n"],"mappings":";AACO,SAAS,mBACd,YACA,aACA,eACU;AACV,QAAM,kBAAkB,YAAY,QAAQ,CAAC,UAAU;AAAA,IACrD;AAAA,IACA;AAAA,EACF,CAAC;AAQD,QAAM,uBAAuB,gBACzB,CAAC,YAAY,2BAA2B,aAAa,IACrD,CAAC;AAEL,QAAM,sBAAsB,gBAAgB,WAAW,IAAI,WAAW;AAEtE,SAAO,WACJ,OAAO,CAAC,SAAS,mBAAmB,CAAC,EACrC,OAAO,eAAe,EACtB,OAAO,CAAC,oBAAoB,CAAC,EAC7B,OAAO,oBAAoB;AAChC;;;AC3BA,YAAY,iBAAiB;AAC7B,YAAY,iBAAiB;AAC7B,SAAS,cAAc,cAAc;AAErC,IAAM,0BAA0B;AAEhC,IAAM,wBAAN,cAAoC,aAAa;AAAA,EAM/C,cAAc;AACZ,UAAM;AAAA,MACJ,MAAM;AAAA,MACN,YAAY;AAAA,MACZ,YAAY;AAAA,IACd,CAAC;AAED,SAAK,gBAAgB,OAAO,UAAU,YAAY;AAClD,SAAK,cAAc,OAAO,kBAAkB,UAAU,OAAO;AAC7D,SAAK,aAAa,OAAO,kBAAkB,eAAe,OAAO;AACjE,SAAK,iBAAiB,OAAO,gBAAgB,mBAAmB;AAAA,EAClE;AAAA,EAEA,MAAM,OAAsB;AAC1B,UAAM,KAAK,OAAO;AAAA,EACpB;AAAA;AAAA,EAGA,MAAM,OAAsB;AAAA,EAAC;AAAA,EAE7B,MAAM,SAAwB;AAM5B,UAAM,iBAA2B;AAAA,MAC/B,KAAK;AAAA,MACL,KAAK;AAAA,MACL,KAAK;AAAA,IACP;AAEA,IAAY;AAAA,MACV,KAAK,UAAU;AAAA,QACb,SAAS,KAAK;AAAA,QACd,QAAQ,KAAK;AAAA,QACb,SAAS,KAAK;AAAA,QACd,MAAM;AAAA,MACR,CAAC;AAAA,IACH;AAEA,UAAM,cAAuC;AAAA,MAC3C,KAAK,KAAK,mBAAmB,OAAO,KAAK,iBAAiB;AAAA,MAC1D,kBAAkB;AAAA,IACpB;AAEA,UAAM,WAAW,MAAkB,iBAAK,OAAO,gBAAgB,WAAW;AAE1E,QAAI,aAAa,GAAG;AAClB,WAAK,YAAY,yBAAyB;AAAA,QACxC;AAAA,MACF,CAAC;AACD,MAAY,sBAAU,yBAAyB,QAAQ,WAAW;AAAA,IACpE,OAAO;AACL,MAAY,iBAAK,0CAA0C;AAAA,IAC7D;AAAA,EACF;AACF;AAEA,SAAS,OAAa;AACpB,MAAI,sBAAsB,EAAE,QAAQ;AACtC;AAEA,KAAK;","names":[]}
\ No newline at end of file
diff --git a/src/nix.test.ts b/src/nix.test.ts
index ebc7640..88ed86f 100644
--- a/src/nix.test.ts
+++ b/src/nix.test.ts
@@ -12,6 +12,14 @@ type TestCase = {
 
 test("Nix command arguments", () => {
   const testCases: TestCase[] = [
+    {
+      inputs: {
+        nixOptions: [],
+        flakeInputs: [],
+        commitMessage: "",
+      },
+      expected: ["flake", "update", "--commit-lock-file"],
+    },
     {
       inputs: {
         nixOptions: ["--log-format", "raw"],
diff --git a/src/nix.ts b/src/nix.ts
index e3d829a..3478aea 100644
--- a/src/nix.ts
+++ b/src/nix.ts
@@ -15,11 +15,9 @@ export function makeNixCommandArgs(
   // configured via `--option <alias name> <option value>`
   // (https://github.com/NixOS/nix/issues/10989).
   // So, we go the long way so that we can support versions both before and after Nix 2.23.0.
-  const lockfileSummaryFlags = [
-    "--option",
-    "commit-lockfile-summary",
-    commitMessage,
-  ];
+  const lockfileSummaryFlags = commitMessage
+    ? ["--option", "commit-lockfile-summary", commitMessage]
+    : [];
 
   const updateLockMechanism = flakeInputFlags.length === 0 ? "update" : "lock";