diff --git a/configure b/configure
index c29cb1040e0..e124bfe5cc0 100755
--- a/configure
+++ b/configure
@@ -12443,6 +12443,28 @@ _ACEOF
 fi
 done
 
+# strto[u]ll may exist but not be declared
+ac_fn_c_check_decl "$LINENO" "strtoll" "ac_cv_have_decl_strtoll" "$ac_includes_default"
+if test "x$ac_cv_have_decl_strtoll" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_STRTOLL $ac_have_decl
+_ACEOF
+ac_fn_c_check_decl "$LINENO" "strtoull" "ac_cv_have_decl_strtoull" "$ac_includes_default"
+if test "x$ac_cv_have_decl_strtoull" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_STRTOULL $ac_have_decl
+_ACEOF
+
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for builtin locking functions" >&5
 $as_echo_n "checking for builtin locking functions... " >&6; }
diff --git a/configure.in b/configure.in
index 79a2649c52b..5b29f56cf7c 100644
--- a/configure.in
+++ b/configure.in
@@ -1546,6 +1546,8 @@ fi
 
 AC_CHECK_FUNCS([strtoll strtoq], [break])
 AC_CHECK_FUNCS([strtoull strtouq], [break])
+# strto[u]ll may exist but not be declared
+AC_CHECK_DECLS([strtoll, strtoull])
 
 AC_CACHE_CHECK([for builtin locking functions], pgac_cv_gcc_int_atomics,
 [AC_TRY_LINK([],
diff --git a/src/include/c.h b/src/include/c.h
index 0976ddffd87..f4480a80bdb 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -960,6 +960,14 @@ __attribute__((format(PG_PRINTF_ATTRIBUTE, 3, 4)));
 extern int	vsnprintf(char *str, size_t count, const char *fmt, va_list args);
 #endif
 
+#if defined(HAVE_LONG_LONG_INT) && defined(HAVE_STRTOLL) && !HAVE_DECL_STRTOLL
+extern long long strtoll(const char *str, char **endptr, int base);
+#endif
+
+#if defined(HAVE_LONG_LONG_INT) && defined(HAVE_STRTOULL) && !HAVE_DECL_STRTOULL
+extern unsigned long long strtoull(const char *str, char **endptr, int base);
+#endif
+
 #if !defined(HAVE_MEMMOVE) && !defined(memmove)
 #define memmove(d, s, c)		bcopy(s, d, c)
 #endif
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 4c8aa0c571b..04cc3f0e37b 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -135,6 +135,14 @@
    don't. */
 #undef HAVE_DECL_STRLCPY
 
+/* Define to 1 if you have the declaration of `strtoll', and to 0 if you
+   don't. */
+#undef HAVE_DECL_STRTOLL
+
+/* Define to 1 if you have the declaration of `strtoull', and to 0 if you
+   don't. */
+#undef HAVE_DECL_STRTOULL
+
 /* Define to 1 if you have the declaration of `sys_siglist', and to 0 if you
    don't. */
 #undef HAVE_DECL_SYS_SIGLIST
diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32
index a39c0a547b3..e3d9bae35fd 100644
--- a/src/include/pg_config.h.win32
+++ b/src/include/pg_config.h.win32
@@ -96,6 +96,14 @@
    don't. */
 #define HAVE_DECL_SNPRINTF 1
 
+/* Define to 1 if you have the declaration of `strtoll', and to 0 if you
+   don't. */
+#define HAVE_DECL_STRTOLL 1
+
+/* Define to 1 if you have the declaration of `strtoull', and to 0 if you
+   don't. */
+#define HAVE_DECL_STRTOULL 1
+
 /* Define to 1 if you have the declaration of `vsnprintf', and to 0 if you
    don't. */
 #define HAVE_DECL_VSNPRINTF 1