diff --git a/crypto/asn1/asn1_test.cc b/crypto/asn1/asn1_test.cc
index 2f0ec76..7d9688b 100644
--- a/crypto/asn1/asn1_test.cc
+++ b/crypto/asn1/asn1_test.cc
@@ -1047,6 +1047,32 @@
   }
 }
 
+TEST(ASN1Test, AdjTime) {
+  struct tm tm1, tm2;
+  int days, secs;
+
+  OPENSSL_posix_to_tm(0, &tm1);
+  OPENSSL_posix_to_tm(0, &tm2);
+  // Test values that are too large and should be rejected.
+  EXPECT_FALSE(OPENSSL_gmtime_adj(&tm1, INT_MIN, INT_MIN));
+  EXPECT_FALSE(OPENSSL_gmtime_adj(&tm1, INT_MAX, INT_MAX));
+  // Basic functionality.
+  EXPECT_TRUE(OPENSSL_gmtime_adj(&tm2, 1, 1));
+  EXPECT_TRUE(OPENSSL_gmtime_diff(&days, &secs, &tm1, &tm2));
+  EXPECT_EQ(days, 1);
+  EXPECT_EQ(secs, 1);
+  EXPECT_TRUE(OPENSSL_gmtime_diff(&days, &secs, &tm2, &tm1));
+  EXPECT_EQ(days, -1);
+  EXPECT_EQ(secs, -1);
+  // Test a value of days that is very large, but valid.
+  EXPECT_TRUE(OPENSSL_gmtime_adj(&tm2, 2932800, 0));
+  EXPECT_TRUE(OPENSSL_gmtime_diff(&days, &secs, &tm1, &tm2));
+  EXPECT_EQ(days, 2932801);
+  EXPECT_EQ(secs, 1);
+  EXPECT_TRUE(OPENSSL_gmtime_diff(&days, &secs, &tm2, &tm1));
+  EXPECT_EQ(days, -2932801);
+  EXPECT_EQ(secs, -1);
+}
 static std::vector<uint8_t> StringToVector(const std::string &str) {
   return std::vector<uint8_t>(str.begin(), str.end());
 }
diff --git a/crypto/asn1/internal.h b/crypto/asn1/internal.h
index 882b5fb..4f98a1a 100644
--- a/crypto/asn1/internal.h
+++ b/crypto/asn1/internal.h
@@ -96,7 +96,8 @@
 // |offset_day| days and |offset_sec| seconds. It returns zero on failure. |tm|
 // must be in the range of year 0000 to 9999 both before and after the update or
 // a failure will be returned.
-int OPENSSL_gmtime_adj(struct tm *tm, int offset_day, long offset_sec);
+OPENSSL_EXPORT int OPENSSL_gmtime_adj(struct tm *tm, int offset_day,
+                                      long offset_sec);
 
 // OPENSSL_gmtime_diff calculates the difference between |from| and |to|. It
 // returns one, and outputs the difference as a number of days and seconds in
diff --git a/crypto/asn1/posix_time.c b/crypto/asn1/posix_time.c
index 81fbe83..7dd9e5b 100644
--- a/crypto/asn1/posix_time.c
+++ b/crypto/asn1/posix_time.c
@@ -191,9 +191,10 @@
                            tm->tm_hour, tm->tm_min, tm->tm_sec, &posix_time)) {
     return 0;
   }
-  if (!utc_from_posix_time(posix_time + off_day * SECS_PER_DAY + offset_sec,
-                           &tm->tm_year, &tm->tm_mon, &tm->tm_mday,
-                           &tm->tm_hour, &tm->tm_min, &tm->tm_sec)) {
+  if (!utc_from_posix_time(
+          posix_time + (int64_t)off_day * SECS_PER_DAY + offset_sec,
+          &tm->tm_year, &tm->tm_mon, &tm->tm_mday, &tm->tm_hour, &tm->tm_min,
+          &tm->tm_sec)) {
     return 0;
   }
   tm->tm_year -= 1900;