diff --git a/lib/strtoofft.h b/lib/strtoofft.h
index 7ebe4f050..b53d1cb52 100644
--- a/lib/strtoofft.h
+++ b/lib/strtoofft.h
@@ -45,6 +45,7 @@
 
 /* For MSVC7 we can use _strtoi64() which seems to be a strtoll() clone */
 #if defined(_MSC_VER) && (_MSC_VER >= 1300)
+_CRTIMP __int64 __cdecl _strtoi64(const char *, char **, int);  /* in <crt/stdlib.h> */
 #define curlx_strtoofft _strtoi64
 #else /* MSVC7 or later */
 curl_off_t curlx_strtoll(const char *nptr, char **endptr, int base);