diff --git a/android/src/main/java/io/invertase/firebase/firestore/FirestoreSerialize.java b/android/src/main/java/io/invertase/firebase/firestore/FirestoreSerialize.java
index 8139e527..982189b5 100644
--- a/android/src/main/java/io/invertase/firebase/firestore/FirestoreSerialize.java
+++ b/android/src/main/java/io/invertase/firebase/firestore/FirestoreSerialize.java
@@ -31,8 +31,6 @@ import io.invertase.firebase.Utils;
 
 public class FirestoreSerialize {
   private static final String TAG = "FirestoreSerialize";
-  private static final DateFormat READ_DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
-  private static final DateFormat WRITE_DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ");
   private static final String KEY_CHANGES = "changes";
   private static final String KEY_DATA = "data";
   private static final String KEY_DOC_CHANGE_DOCUMENT = "document";
@@ -43,12 +41,6 @@ public class FirestoreSerialize {
   private static final String KEY_METADATA = "metadata";
   private static final String KEY_PATH = "path";
 
-  static {
-    // Javascript Date.toISOString is always formatted to UTC
-    // We set the read TimeZone to UTC to account for this
-    READ_DATE_FORMAT.setTimeZone(TimeZone.getTimeZone("UTC"));
-  }
-
   /**
    * Convert a DocumentSnapshot instance into a React Native WritableMap
    *
@@ -220,7 +212,7 @@ public class FirestoreSerialize {
         typeMap.putMap("value", geoPoint);
       } else if (value instanceof Date) {
         typeMap.putString("type", "date");
-        typeMap.putString("value", WRITE_DATE_FORMAT.format((Date) value));
+        typeMap.putDouble("value", ((Date) value).getTime());
       } else {
         // TODO: Changed to log an error rather than crash - is this correct?
         Log.e(TAG, "buildTypeMap: Cannot convert object of type " + value.getClass());
@@ -275,13 +267,8 @@ public class FirestoreSerialize {
       ReadableMap geoPoint = typeMap.getMap("value");
       return new GeoPoint(geoPoint.getDouble("latitude"), geoPoint.getDouble("longitude"));
     } else if ("date".equals(type)) {
-      try {
-        String date = typeMap.getString("value");
-        return READ_DATE_FORMAT.parse(date);
-      } catch (ParseException exception) {
-        Log.e(TAG, "parseTypeMap", exception);
-        return null;
-      }
+      Double time = typeMap.getDouble("value");
+      return new Date(time.longValue());
     } else if ("fieldvalue".equals(type)) {
       String value = typeMap.getString("value");
       if ("delete".equals(value)) {
diff --git a/ios/RNFirebase/firestore/RNFirebaseFirestoreDocumentReference.m b/ios/RNFirebase/firestore/RNFirebaseFirestoreDocumentReference.m
index caa5495f..cd04347d 100644
--- a/ios/RNFirebase/firestore/RNFirebaseFirestoreDocumentReference.m
+++ b/ios/RNFirebase/firestore/RNFirebaseFirestoreDocumentReference.m
@@ -205,9 +205,9 @@ static NSMutableDictionary *_listeners;
         typeMap[@"value"] = geopoint;
     } else if ([value isKindOfClass:[NSDate class]]) {
         typeMap[@"type"] = @"date";
-        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
-        [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSSZ"];
-        typeMap[@"value"] = [dateFormatter stringFromDate:(NSDate *)value];
+        // NOTE: The round() is important as iOS ends up giving .999 otherwise,
+        // and loses a millisecond when going between native and JS
+        typeMap[@"value"] = @(round([(NSDate *)value timeIntervalSince1970] * 1000.0));
     } else if ([value isKindOfClass:[NSNumber class]]) {
         NSNumber *number = (NSNumber *)value;
         if (number == (void*)kCFBooleanFalse || number == (void*)kCFBooleanTrue) {
@@ -262,9 +262,7 @@ static NSMutableDictionary *_listeners;
         NSNumber *longitude = geopoint[@"longitude"];
         return [[FIRGeoPoint alloc] initWithLatitude:[latitude doubleValue] longitude:[longitude doubleValue]];
     } else if ([type isEqualToString:@"date"]) {
-        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
-        [dateFormatter setDateFormat:@"yyyy-MM-dd'T'HH:mm:ss.SSSZ"];
-        return [dateFormatter dateFromString:value];
+        return [NSDate dateWithTimeIntervalSince1970:([(NSNumber *)value doubleValue] / 1000.0)];
     } else if ([type isEqualToString:@"fieldvalue"]) {
         NSString *string = (NSString*)value;
         if ([string isEqualToString:@"delete"]) {
diff --git a/lib/modules/firestore/utils/serialize.js b/lib/modules/firestore/utils/serialize.js
index 3ef0b09a..5bdebf26 100644
--- a/lib/modules/firestore/utils/serialize.js
+++ b/lib/modules/firestore/utils/serialize.js
@@ -67,7 +67,7 @@ const buildTypeMap = (value: any): any => {
       };
     } else if (value instanceof Date) {
       typeMap.type = 'date';
-      typeMap.value = value.toISOString();
+      typeMap.value = value.getTime();
     } else {
       typeMap.type = 'object';
       typeMap.value = buildNativeMap(value);
diff --git a/tests/src/tests/firestore/documentReferenceTests.js b/tests/src/tests/firestore/documentReferenceTests.js
index 968cb28b..a6aa2f65 100644
--- a/tests/src/tests/firestore/documentReferenceTests.js
+++ b/tests/src/tests/firestore/documentReferenceTests.js
@@ -435,6 +435,7 @@ function documentReferenceTests({ describe, it, context, firebase }) {
         const doc = await docRef.get();
         doc.data().field.should.be.instanceof(Date);
         should.equal(doc.data().field.toISOString(), date.toISOString());
+        should.equal(doc.data().field.getTime(), date.getTime());
       });
     });