diff --git a/src/tl/tl/tlString.cc b/src/tl/tl/tlString.cc
index d57dee236..7bd12c832 100644
--- a/src/tl/tl/tlString.cc
+++ b/src/tl/tl/tlString.cc
@@ -1975,17 +1975,17 @@ sprintf (const char *f, const std::vector <tl::Variant> &vv, unsigned int a0)
           os.setf (std::ios::uppercase);
         }
         if (a < vv.size ()) {
-          os << vv [a].to_ulong ();
+          os << vv [a].to_ulonglong ();
         }
       } else if (*cp == 'u' || *cp == 'U') {
         os.setf (std::ios_base::fmtflags (0), std::ios::basefield);
         if (a < vv.size ()) {
-          os << vv [a].to_ulong ();
+          os << vv [a].to_ulonglong ();
         }
       } else if (*cp == 'd' || *cp == 'D') {
         os.setf (std::ios_base::fmtflags (0), std::ios::basefield);
         if (a < vv.size ()) {
-          os << vv [a].to_long ();
+          os << vv [a].to_longlong ();
         }
       } else if (*cp == 's' || *cp == 'S') {
         os.setf (std::ios_base::fmtflags (0), std::ios::basefield);
diff --git a/src/tl/unit_tests/tlStringTests.cc b/src/tl/unit_tests/tlStringTests.cc
index 634b38e6e..8d8696b09 100644
--- a/src/tl/unit_tests/tlStringTests.cc
+++ b/src/tl/unit_tests/tlStringTests.cc
@@ -57,6 +57,20 @@ TEST(1)
   EXPECT_EQ (tl::sprintf("%lu %llu %02x", 1, 2, 167), "1 2 a7");
   EXPECT_EQ (tl::sprintf("%lu %llu %02X", 1, 2, 761), "1 2 2F9");
   EXPECT_EQ (tl::sprintf("%c%c", 'a', 'X'), "aX");
+
+  //  64bit numbers
+  EXPECT_EQ (tl::sprintf("%x", 0x1000000000ll), "1000000000");
+  EXPECT_EQ (tl::sprintf("%lx", 0x1000000000ll), "1000000000");
+  EXPECT_EQ (tl::sprintf("%llx", 0x1000000000ll), "1000000000");
+  EXPECT_EQ (tl::sprintf("%d", 100000000000ll), "100000000000");
+  EXPECT_EQ (tl::sprintf("%ld", 100000000000ll), "100000000000");
+  EXPECT_EQ (tl::sprintf("%lld", 100000000000ll), "100000000000");
+  EXPECT_EQ (tl::sprintf("%d", -100000000000ll), "-100000000000");
+  EXPECT_EQ (tl::sprintf("%ld", -100000000000ll), "-100000000000");
+  EXPECT_EQ (tl::sprintf("%lld", -100000000000ll), "-100000000000");
+  EXPECT_EQ (tl::sprintf("%u", 100000000000ull), "100000000000");
+  EXPECT_EQ (tl::sprintf("%lu", 100000000000ull), "100000000000");
+  EXPECT_EQ (tl::sprintf("%llu", 100000000000ull), "100000000000");
 }
 
 TEST(1a)