diff --git a/psutil/_psutil_common.c b/psutil/_psutil_common.c
index 890d515f6..1b83f7508 100644
--- a/psutil/_psutil_common.c
+++ b/psutil/_psutil_common.c
@@ -281,14 +281,16 @@ psutil_loadlibs() {
         "ntdll", "RtlNtStatusToDosErrorNoTeb");
     if (! RtlNtStatusToDosErrorNoTeb)
         return 1;
-
-    // --- Optional
-    // not available on Wine
-    RtlIpv6AddressToStringA = psutil_GetProcAddressFromLib(
-        "ntdll.dll", "RtlIpv6AddressToStringA");
-    // minimum requirement: Win Vista
     GetTickCount64 = psutil_GetProcAddress(
         "kernel32", "GetTickCount64");
+    if (! GetTickCount64)
+        return 1;
+    RtlIpv6AddressToStringA = psutil_GetProcAddressFromLib(
+        "ntdll.dll", "RtlIpv6AddressToStringA");
+    if (! RtlIpv6AddressToStringA)
+        return 1;
+
+    // --- Optional
     // minimum requirement: Win 7
     GetActiveProcessorCount = psutil_GetProcAddress(
         "kernel32", "GetActiveProcessorCount");
diff --git a/psutil/_psutil_windows.c b/psutil/_psutil_windows.c
index dd336489e..d5928d72c 100644
--- a/psutil/_psutil_windows.c
+++ b/psutil/_psutil_windows.c
@@ -101,17 +101,7 @@ psutil_boot_time(PyObject *self, PyObject *args) {
     ll = (((ULONGLONG)
         (fileTime.dwHighDateTime)) << 32) + fileTime.dwLowDateTime;
     pt = (time_t)((ll - 116444736000000000ull) / 10000000ull);
-
-    if (GetTickCount64 != NULL) {
-        // Windows >= Vista
-        uptime = GetTickCount64() / 1000ull;
-    }
-    else {
-        // Windows XP.
-        // GetTickCount() time will wrap around to zero if the
-        // system is run continuously for 49.7 days.
-        uptime = (ULONGLONG)GetTickCount() / 1000ull;
-    }
+    uptime = GetTickCount64() / 1000ull;
     return Py_BuildValue("K", pt - uptime);
 }