diff --git a/e2e/__snapshots__/e2e.spec.ts.snap b/e2e/__snapshots__/e2e.spec.ts.snap
index 2f65c9d..6b5331f 100644
--- a/e2e/__snapshots__/e2e.spec.ts.snap
+++ b/e2e/__snapshots__/e2e.spec.ts.snap
@@ -168,7 +168,10 @@ exports[`e2e tests [snapshot] ruleset with unversioned module in source 1`] = `
 "----------------------------------------------------
 modules/unversioned/1.0.0/MODULE.bazel
 ----------------------------------------------------
-module(name = \\"unversioned\\", version = \\"1.0.0\\")
+module(
+    name = \\"unversioned\\",
+  version = \\"1.0.0\\"
+)
 
 ----------------------------------------------------
 modules/unversioned/1.0.0/patches/module_dot_bazel_version.patch
@@ -176,9 +179,12 @@ modules/unversioned/1.0.0/patches/module_dot_bazel_version.patch
 ===================================================================
 --- a/MODULE.bazel
 +++ b/MODULE.bazel
-@@ -1,1 +1,1 @@
--module(name = \\"unversioned\\")
-+module(name = \\"unversioned\\", version = \\"1.0.0\\")
+@@ -1,3 +1,4 @@
+ module(
+-    name = \\"unversioned\\"
++    name = \\"unversioned\\",
++  version = \\"1.0.0\\"
+ )
 
 ----------------------------------------------------
 modules/unversioned/1.0.0/presubmit.yml
@@ -198,11 +204,11 @@ bcr_test_module:
 modules/unversioned/1.0.0/source.json
 ----------------------------------------------------
 {
-    \\"integrity\\": \\"sha256-X2ZIYATg3qceheFSj/qaTU0SqqW/hFc8UIGkrK3FmZQ=\\",
+    \\"integrity\\": \\"sha256-oLg/mgWyhr6DFepRYkjoPphQ8KOriLgu6M4x2RSsLbU=\\",
     \\"strip_prefix\\": \\"unversioned-1.0.0\\",
     \\"url\\": \\"https://github.com/testorg/unversioned/archive/refs/tags/v1.0.0.tar.gz\\",
     \\"patches\\": {
-        \\"module_dot_bazel_version.patch\\": \\"sha256-OoXz9ahBlGjW4IVb4QCmXMZInK7XbFEjCHya3wx8AAk=\\"
+        \\"module_dot_bazel_version.patch\\": \\"sha256-CahdP4+xcGJVM9GyA0Sg2rUe5rIPHzKJ6J4SfFTm2x8=\\"
     },
     \\"patch_strip\\": 1
 }
@@ -326,7 +332,7 @@ bcr_test_module:
 modules/zero-versioned/1.0.0/source.json
 ----------------------------------------------------
 {
-    \\"integrity\\": \\"sha256-P4olS5x2mo1PJPI6iU0TMfPHWs9inbRZFJZHmhEY4no=\\",
+    \\"integrity\\": \\"sha256-sLh05DKTEOuO3vz9+IDUJJNOf0GSLxdGDJ8qOLZRUCQ=\\",
     \\"strip_prefix\\": \\"zero-versioned-1.0.0\\",
     \\"url\\": \\"https://github.com/testorg/zero-versioned/archive/refs/tags/v1.0.0.tar.gz\\",
     \\"patches\\": {
diff --git a/e2e/fixtures/unversioned/MODULE.bazel b/e2e/fixtures/unversioned/MODULE.bazel
index e00336e..93d4911 100644
--- a/e2e/fixtures/unversioned/MODULE.bazel
+++ b/e2e/fixtures/unversioned/MODULE.bazel
@@ -1 +1,3 @@
-module(name = "unversioned")
+module(
+    name = "unversioned"
+)
diff --git a/e2e/fixtures/zero-versioned/README.md b/e2e/fixtures/zero-versioned/README.md
index d1da306..6322257 100644
--- a/e2e/fixtures/zero-versioned/README.md
+++ b/e2e/fixtures/zero-versioned/README.md
@@ -1 +1 @@
-Ruleset repo that doesn't update the source MODULE.bazel's `version` field.
+Ruleset repo that doesn't set the source MODULE.bazel's `version` field.
diff --git a/src/domain/module-file.spec.ts b/src/domain/module-file.spec.ts
index bc42d49..e6afda1 100644
--- a/src/domain/module-file.spec.ts
+++ b/src/domain/module-file.spec.ts
@@ -36,11 +36,19 @@ describe("moduleName", () => {
   });
 });
 
-describe("moduleVersion", () => {
+describe("version", () => {
   test("parses module version", () => {
     const moduleFile = new ModuleFile("MODULE.bazel");
     expect(moduleFile.version).toEqual("1.2.3");
   });
+
+  test("returns undefined when the version is missing", () => {
+    mocked(fs.readFileSync).mockReturnValue(`\
+module(name = "rules_foo")
+`);
+    const moduleFile = new ModuleFile("MODULE.bazel");
+    expect(moduleFile.version).toBeUndefined();
+  });
 });
 
 describe("content", () => {
@@ -60,6 +68,21 @@ describe("stampVersion", () => {
       fakeModuleFile({ moduleName: "rules_foo", version: "4.5.6" })
     );
   });
+
+  test("stamps the version when the version field was originally missing", () => {
+    mocked(fs.readFileSync).mockReturnValue(`\
+module(
+  name = "rules_foo",
+)`);
+    const moduleFile = new ModuleFile("MODULE.bazel");
+    moduleFile.stampVersion("4.5.6");
+
+    expect(moduleFile.content).toEqual(`\
+module(
+  name = "rules_foo",
+  version = "4.5.6"
+)`);
+  });
 });
 
 describe("save", () => {
diff --git a/src/domain/module-file.ts b/src/domain/module-file.ts
index 36817ac..7c0b368 100644
--- a/src/domain/module-file.ts
+++ b/src/domain/module-file.ts
@@ -21,10 +21,10 @@ export class ModuleFile {
     return name;
   }
 
-  public get version(): string {
+  public get version(): string | undefined {
     const regex = /module\([^)]*?version\s*=\s*"(.+?)"/s;
     const match = this.moduleContent.match(regex);
-    return match ? match[1] : "";
+    return match ? match[1] : undefined;
   }
 
   public get content(): string {
@@ -32,7 +32,7 @@ export class ModuleFile {
   }
 
   public stampVersion(version: string): void {
-    if (this.version) {
+    if (this.version !== undefined) {
       // update the version
       this.moduleContent = this.moduleContent.replace(
         /(^.*?module\(.*?version\s*=\s*")[\w.]+(".*$)/s,
@@ -41,8 +41,8 @@ export class ModuleFile {
     } else {
       // add the version
       this.moduleContent = this.moduleContent.replace(
-        /(^.*?module\(.*?)\)/s,
-        `$1, version = "${version}")`
+        /(^.*?module\(.*?)(\s*)\)/s,
+        `$1,\n  version = "${version}"\n)`
       );
     }
   }