diff --git a/README.md b/README.md
index 92bcf3e7..2e582db7 100644
--- a/README.md
+++ b/README.md
@@ -154,6 +154,10 @@ Given those constraints, version numbers follow standard SemVer, with the follow
 
 ## Changelog
 
+### v2.12.0
+
+* 🐛 Fixed [`gps.toDate is not a function`](https://github.com/mceachen/exiftool-vendored.js/issues/3)
+
 ### v2.11.0
 
 * 🌱 ExifTool upgraded to v10.47
diff --git a/src/tags_task.spec.ts b/src/tags_task.spec.ts
index 4addf8bc..3468ab2f 100644
--- a/src/tags_task.spec.ts
+++ b/src/tags_task.spec.ts
@@ -75,6 +75,14 @@ describe("TimeZone extraction", () => {
     expect(t.DateTimeOriginal.tzoffsetMinutes).to.eql(8 * 60)
     expect(t.DateTimeCreated.tzoffsetMinutes).to.eql(8 * 60)
   })
+
+  it("skips invalid timestamps", () => {
+    const t = parse({
+      DateTimeOriginal: "2016:08:12 13:28:50",
+      GPSDateTime: "not a timestamp",
+    })
+    expect(t.DateTimeOriginal.tzoffsetMinutes).to.be.undefined
+  })
 })
 
 describe("SubSecDateTimeOriginal", () => {
diff --git a/src/tags_task.ts b/src/tags_task.ts
index b545fc28..c9108df5 100644
--- a/src/tags_task.ts
+++ b/src/tags_task.ts
@@ -46,14 +46,14 @@ export class TagsTask extends Task<Tags> {
   }
 
   private extractTzoffset(): void {
-    // TimeZone just wins if we're just handed it, then use it:
+    // TimeZone wins if we've got it:
     const tze = new _dt.ExifTimeZoneOffset("TimeZone", this.rawTags.TimeZone)
     if (tze.tzOffsetMinutes !== undefined) {
       this.tzoffset = tze.tzOffsetMinutes
-    } else {
+    } else if (this.rawTags.GPSDateTime != null && this.rawTags.DateTimeOriginal != null) {
       const gps = _dt.parse("GPSDateTime", this.rawTags.GPSDateTime, 0) as _dt.ExifDateTime
       const local = _dt.parse("DateTimeOriginal", this.rawTags.DateTimeOriginal, 0) as _dt.ExifDateTime
-      if (gps && local) {
+      if (gps && local && gps.toDate && local.toDate) {
         // timezone offsets are never less than 30 minutes.
         const gpsToHalfHour = gps.toDate().getTime() / (30 * 60 * 1000)
         const localToHalfHour = local.toDate().getTime() / (30 * 60 * 1000)