diff --git a/hmac_utils.cpp b/hmac_utils.cpp
index da4ee8d..fd0c9a7 100644
--- a/hmac_utils.cpp
+++ b/hmac_utils.cpp
@@ -36,8 +36,12 @@ namespace hmac {
         }
         std::time_t rounded = (now / interval_sec) * interval_sec;
         if (constant_time_equals(token, get_hmac(key, std::to_string(rounded), hash_type))) return true;
-        if (constant_time_equals(token, get_hmac(key, std::to_string(rounded - interval_sec), hash_type))) return true;
-        if (constant_time_equals(token, get_hmac(key, std::to_string(rounded + interval_sec), hash_type))) return true;
+        if (rounded >= std::numeric_limits<std::time_t>::min() + interval_sec) {
+            if (constant_time_equals(token, get_hmac(key, std::to_string(rounded - interval_sec), hash_type))) return true;
+        }
+        if (rounded <= std::numeric_limits<std::time_t>::max() - interval_sec) {
+            if (constant_time_equals(token, get_hmac(key, std::to_string(rounded + interval_sec), hash_type))) return true;
+        }
         return false;
     }
 
@@ -66,10 +70,14 @@ namespace hmac {
         std::string prefix = "|" + fingerprint;
         std::string payload = std::to_string(rounded) + prefix;
         if (constant_time_equals(token, get_hmac(key, payload, hash_type))) return true;
-        payload = std::to_string(rounded - interval_sec) + prefix;
-        if (constant_time_equals(token, get_hmac(key, payload, hash_type))) return true;
-        payload = std::to_string(rounded + interval_sec) + prefix;
-        if (constant_time_equals(token, get_hmac(key, payload, hash_type))) return true;
+        if (rounded >= std::numeric_limits<std::time_t>::min() + interval_sec) {
+            payload = std::to_string(rounded - interval_sec) + prefix;
+            if (constant_time_equals(token, get_hmac(key, payload, hash_type))) return true;
+        }
+        if (rounded <= std::numeric_limits<std::time_t>::max() - interval_sec) {
+            payload = std::to_string(rounded + interval_sec) + prefix;
+            if (constant_time_equals(token, get_hmac(key, payload, hash_type))) return true;
+        }
         return false;
     }
 
diff --git a/test_all.cpp b/test_all.cpp
index 91e8777..fb61991 100644
--- a/test_all.cpp
+++ b/test_all.cpp
@@ -1,9 +1,16 @@
 #include <gtest/gtest.h>
 #include <string>
 #include <stdexcept>
+#include <limits>
 #include "hmac.hpp"
 #include "hmac_utils.hpp"
 
+static std::time_t mock_time_value = 0;
+extern "C" std::time_t time(std::time_t* t) {
+    if (t) *t = mock_time_value;
+    return mock_time_value;
+}
+
 TEST(HashTest, SHA1) {
     EXPECT_EQ(hmac_hash::sha1("grape"),
               "bc8a2f8cdedb005b5c787692853709b060db75ff");
@@ -65,6 +72,56 @@ TEST(TokenTest, InvalidInterval) {
     EXPECT_THROW(hmac::is_token_valid(token, key, 0), std::invalid_argument);
 }
 
+TEST(TokenBoundaryTest, MaxTime) {
+    const std::string key = "12345";
+    const int interval = 30;
+    mock_time_value = std::numeric_limits<std::time_t>::max();
+    std::string token = hmac::generate_time_token(key, interval);
+    EXPECT_TRUE(hmac::is_token_valid(token, key, interval));
+    mock_time_value = std::numeric_limits<std::time_t>::max() - interval;
+    std::string token_prev = hmac::generate_time_token(key, interval);
+    mock_time_value = std::numeric_limits<std::time_t>::max();
+    EXPECT_TRUE(hmac::is_token_valid(token_prev, key, interval));
+}
+
+TEST(TokenBoundaryTest, MinTime) {
+    const std::string key = "12345";
+    const int interval = 30;
+    mock_time_value = std::numeric_limits<std::time_t>::min();
+    std::string token = hmac::generate_time_token(key, interval);
+    EXPECT_TRUE(hmac::is_token_valid(token, key, interval));
+    mock_time_value = std::numeric_limits<std::time_t>::min() + interval;
+    std::string token_next = hmac::generate_time_token(key, interval);
+    mock_time_value = std::numeric_limits<std::time_t>::min();
+    EXPECT_TRUE(hmac::is_token_valid(token_next, key, interval));
+}
+
+TEST(TokenBoundaryFingerprintTest, MaxTime) {
+    const std::string key = "12345";
+    const std::string fingerprint = "fp";
+    const int interval = 30;
+    mock_time_value = std::numeric_limits<std::time_t>::max();
+    std::string token = hmac::generate_time_token(key, fingerprint, interval);
+    EXPECT_TRUE(hmac::is_token_valid(token, key, fingerprint, interval));
+    mock_time_value = std::numeric_limits<std::time_t>::max() - interval;
+    std::string token_prev = hmac::generate_time_token(key, fingerprint, interval);
+    mock_time_value = std::numeric_limits<std::time_t>::max();
+    EXPECT_TRUE(hmac::is_token_valid(token_prev, key, fingerprint, interval));
+}
+
+TEST(TokenBoundaryFingerprintTest, MinTime) {
+    const std::string key = "12345";
+    const std::string fingerprint = "fp";
+    const int interval = 30;
+    mock_time_value = std::numeric_limits<std::time_t>::min();
+    std::string token = hmac::generate_time_token(key, fingerprint, interval);
+    EXPECT_TRUE(hmac::is_token_valid(token, key, fingerprint, interval));
+    mock_time_value = std::numeric_limits<std::time_t>::min() + interval;
+    std::string token_next = hmac::generate_time_token(key, fingerprint, interval);
+    mock_time_value = std::numeric_limits<std::time_t>::min();
+    EXPECT_TRUE(hmac::is_token_valid(token_next, key, fingerprint, interval));
+}
+
 int main(int argc, char **argv) {
     ::testing::InitGoogleTest(&argc, argv);
     return RUN_ALL_TESTS();