diff --git a/GoogleSignIn/Tests/Unit/GIDAuthenticationTest.m b/GoogleSignIn/Tests/Unit/GIDAuthenticationTest.m
index ad57bead..89f7f982 100644
--- a/GoogleSignIn/Tests/Unit/GIDAuthenticationTest.m
+++ b/GoogleSignIn/Tests/Unit/GIDAuthenticationTest.m
@@ -554,7 +554,7 @@ - (void)observeValueForKeyPath:(NSString *)keyPath
 - (GIDAuthentication *)auth {
   NSString *idToken = [self idToken];
   NSNumber *accessTokenExpiresIn =
-      @(_accessTokenExpireTime - [[NSDate date] timeIntervalSinceReferenceDate]);
+      @(_accessTokenExpireTime - [[NSDate date] timeIntervalSince1970]);
   OIDTokenRequest *tokenRequest =
       [OIDTokenRequest testInstanceWithAdditionalParameters:_additionalTokenRequestParameters];
   OIDTokenResponse *tokenResponse =
@@ -570,7 +570,7 @@ - (NSString *)idTokenWithExpireTime:(NSTimeInterval)expireTime {
   if (!_hasIDToken) {
     return nil;
   }
-  return [OIDTokenResponse idTokenWithSub:kUserID exp:@(expireTime + NSTimeIntervalSince1970)];
+  return [OIDTokenResponse idTokenWithSub:kUserID exp:@(expireTime)];
 }
 
 - (NSString *)idToken {
@@ -595,7 +595,7 @@ - (GIDAuthentication *)observedAuth {
 }
 
 - (OIDTokenResponse *)tokenResponseWithNewTokens {
-  NSNumber *expiresIn = @(kNewExpireTime - [NSDate timeIntervalSinceReferenceDate]);
+  NSNumber *expiresIn = @(kNewExpireTime - [[NSDate date] timeIntervalSince1970]);
   return [OIDTokenResponse testInstanceWithIDToken:(_hasIDToken ? [self idTokenNew] : nil)
                                        accessToken:kNewAccessToken
                                          expiresIn:expiresIn
@@ -607,7 +607,7 @@ - (NSError *)fakeError {
 }
 
 - (void)assertDate:(NSDate *)date equalTime:(NSTimeInterval)time {
-  XCTAssertEqualWithAccuracy([date timeIntervalSinceReferenceDate], time, kTimeAccuracy);
+  XCTAssertEqualWithAccuracy([date timeIntervalSince1970], time, kTimeAccuracy);
 }
 
 - (void)assertOldAccessTokenInAuth:(GIDAuthentication *)auth {
@@ -643,8 +643,8 @@ - (void)setTokensExpireTime:(NSTimeInterval)fromNow {
 }
 
 - (void)setExpireTimeForAccessToken:(NSTimeInterval)accessExpire IDToken:(NSTimeInterval)idExpire {
-  _accessTokenExpireTime = [[NSDate date] timeIntervalSinceReferenceDate] + accessExpire;
-  _idTokenExpireTime = [[NSDate date] timeIntervalSinceReferenceDate] + idExpire;
+  _accessTokenExpireTime = [[NSDate date] timeIntervalSince1970] + accessExpire;
+  _idTokenExpireTime = [[NSDate date] timeIntervalSince1970] + idExpire;
 }
 
 - (void)verifyTokensRefreshedWithMethod:(SEL)sel {
diff --git a/GoogleSignIn/Tests/Unit/GIDGoogleUserTest.m b/GoogleSignIn/Tests/Unit/GIDGoogleUserTest.m
index 2ff9e567..d09ddc5a 100644
--- a/GoogleSignIn/Tests/Unit/GIDGoogleUserTest.m
+++ b/GoogleSignIn/Tests/Unit/GIDGoogleUserTest.m
@@ -99,7 +99,7 @@ - (void)testLegacyCoding {
 #endif // TARGET_OS_IOS || TARGET_OS_MACCATALYST
 
 - (void)testUpdateAuthState {
-  NSTimeInterval accessTokenExpireTime = [NSDate timeIntervalSinceReferenceDate];
+  NSTimeInterval accessTokenExpireTime = [[NSDate date] timeIntervalSince1970];
   NSTimeInterval idTokenExpireTime = accessTokenExpireTime + kTimeIncrement;
   
   NSString *idToken = [self idTokenWithExpireTime:idTokenExpireTime];
@@ -120,18 +120,19 @@ - (void)testUpdateAuthState {
   [user updateAuthState:updatedAuthState profileData:updatedProfileData];
   
   XCTAssertEqualObjects(user.accessToken.tokenString, kNewAccessToken);
-  XCTAssertEqualWithAccuracy([user.accessToken.expirationDate timeIntervalSinceReferenceDate],
+  XCTAssertEqualWithAccuracy([user.accessToken.expirationDate timeIntervalSince1970],
                              updatedAccessTokenExpireTime, kTimeAccuracy);
   XCTAssertEqualObjects(user.idToken.tokenString, updatedIDToken);
-  XCTAssertEqualWithAccuracy([user.idToken.expirationDate timeIntervalSinceReferenceDate],
+  XCTAssertEqualWithAccuracy([user.idToken.expirationDate timeIntervalSince1970],
                              updatedIDTokenExpireTime, kTimeAccuracy);
   XCTAssertEqual(user.profile, updatedProfileData);
 }
 
 #pragma mark - Helpers
 
+// The expireTime should be based on 1970.
 - (NSString *)idTokenWithExpireTime:(NSTimeInterval)expireTime {
-  return [OIDTokenResponse idTokenWithSub:kUserID exp:@(expireTime + NSTimeIntervalSince1970)];
+  return [OIDTokenResponse idTokenWithSub:kUserID exp:@(expireTime)];
 }
 
 @end
diff --git a/GoogleSignIn/Tests/Unit/OIDAuthState+Testing.m b/GoogleSignIn/Tests/Unit/OIDAuthState+Testing.m
index 6c019820..9143c4f7 100644
--- a/GoogleSignIn/Tests/Unit/OIDAuthState+Testing.m
+++ b/GoogleSignIn/Tests/Unit/OIDAuthState+Testing.m
@@ -37,7 +37,7 @@ + (instancetype)testInstanceWithIDToken:(NSString *)idToken
                             accessToken:(NSString *)accessToken
                   accessTokenExpireTime:(NSTimeInterval)accessTokenExpireTime {
   NSNumber *accessTokenExpiresIn =
-      @(accessTokenExpireTime - [[NSDate date] timeIntervalSinceReferenceDate]);
+      @(accessTokenExpireTime - [[NSDate date] timeIntervalSince1970]);
   OIDTokenResponse *newResponse =
       [OIDTokenResponse testInstanceWithIDToken:idToken
                                     accessToken:accessToken
diff --git a/GoogleSignIn/Tests/Unit/OIDTokenResponse+Testing.h b/GoogleSignIn/Tests/Unit/OIDTokenResponse+Testing.h
index 990fda0f..dc30523c 100644
--- a/GoogleSignIn/Tests/Unit/OIDTokenResponse+Testing.h
+++ b/GoogleSignIn/Tests/Unit/OIDTokenResponse+Testing.h
@@ -62,6 +62,10 @@ extern NSString * const kFatPictureURL;
 
 + (NSString *)fatIDToken;
 
+/**
+ * @sub The subject of the ID token.
+ * @exp The interval between 00:00:00 UTC on 1 January 1970 and the expiration date of the ID token.
+ */
 + (NSString *)idTokenWithSub:(NSString *)sub exp:(NSNumber *)exp;
 
 + (NSString *)idTokenWithSub:(NSString *)sub exp:(NSNumber *)exp fat:(BOOL)fat;