diff --git a/src/librepgp/stream-sig.cpp b/src/librepgp/stream-sig.cpp
index cba39f7ff..40e676e9e 100644
--- a/src/librepgp/stream-sig.cpp
+++ b/src/librepgp/stream-sig.cpp
@@ -73,7 +73,7 @@ signature_hash_key(const pgp_key_pkt_t &key, rnp::Hash &hash, pgp_version_t pgpv
         break;
     }
     case PGP_V5: {
-        assert(key.pub_data.size() < ((size_t) 1 << 32));
+        assert(key.pub_data.size() < ((uint64_t) 1 << 32));
         uint8_t hdr[5] = {0x9A, 0x00, 0x00, 0x00, 0x00};
         write_uint32(hdr + 1, key.pub_data.size());
         hash.add(&hdr, 5);
@@ -82,7 +82,7 @@ signature_hash_key(const pgp_key_pkt_t &key, rnp::Hash &hash, pgp_version_t pgpv
     }
 #if defined(ENABLE_CRYPTO_REFRESH)
     case PGP_V6: {
-        assert(key.pub_data.size() < ((size_t) 1 << 32));
+        assert(key.pub_data.size() < ((uint64_t) 1 << 32));
         uint8_t hdr[5] = {0x9b, 0x00, 0x00, 0x00, 0x00};
         write_uint32(hdr + 1, key.pub_data.size());
         hash.add(hdr, sizeof(hdr));
diff --git a/src/tests/cli_tests.py b/src/tests/cli_tests.py
index 9ffdef585..93277cf70 100755
--- a/src/tests/cli_tests.py
+++ b/src/tests/cli_tests.py
@@ -10,6 +10,7 @@
 import time
 import unittest
 import random
+import ctypes
 from platform import architecture
 
 from cli_common import (file_text, find_utility, is_windows, list_upto,
@@ -61,6 +62,13 @@ def escape_regex(str):
     return '^' + ''.join((c, "[\\x{:02X}]".format(ord(c)))[0 <= ord(c) <= 0x20 \
         or c in ['[',']','(',')','|','"','$','.','*','^','$','\\','+','?','{','}']] for c in str) + '$'
 
+def time_t_is_greater_than_32bit() -> bool:
+    if hasattr(ctypes, 'c_time_t'):
+        return ctypes.sizeof(ctypes.c_time_t) > 4
+    else:
+        # probably Python < 3.12, just guess based on sys.maxsize
+        return sys.maxsize > 2 ** 32
+
 UNICODE_LATIN_CAPITAL_A_GRAVE = unichr(192)
 UNICODE_LATIN_SMALL_A_GRAVE = unichr(224)
 UNICODE_LATIN_CAPITAL_A_MACRON = unichr(256)
@@ -3761,7 +3769,6 @@ def test_interactive_password(self):
 
     def test_set_current_time(self):
         # Too old date
-        is64bit = sys.maxsize > 2 ** 32
         gparam = ['--homedir', RNPDIR2, '--notty', '--password', PASSWORD, '--generate-key', '--numbits', '1024', '--current-time']
         rparam = ['--homedir', RNPDIR2, '--notty', '--remove-key']
         ret, out, err = run_proc(RNPK, gparam + ['1950-01-02', '--userid', 'key-1950'])
@@ -3839,7 +3846,7 @@ def test_set_current_time(self):
 
         # Try too distant date for expiration
         ret, out, err = run_proc(RNPK, gparam + ['2024-02-29', '--expiration', '3024-02-29', '--userid', 'key-2924'])
-        if is64bit:
+        if time_t_is_greater_than_32bit():
             self.assertEqual(ret, 1)
             self.assertRegex(err, r'(?s)^.*Expiration time exceeds 32-bit value.*$')
             self.assertRegex(err, r'(?s)^.*Failed to set primary key expiration..*$')