diff --git a/ext/gmp/tests/gh16870.phpt b/ext/gmp/tests/gh16870.phpt
new file mode 100644
index 0000000000000..2cdbc44f3f1ac
--- /dev/null
+++ b/ext/gmp/tests/gh16870.phpt
@@ -0,0 +1,26 @@
+--TEST--
+Bug GH-16870 (Overly restrictive gmp_pow overflow checks)
+--EXTENSIONS--
+gmp
+--XFAIL--
+Currently fails after the introduction of overflow warning
+--FILE--
+<?php
+echo '64^11 = 0x', gmp_strval(gmp_pow(64, 11), 16), "\n";
+echo '2^31 = 0x', gmp_strval(gmp_pow(2, 31), 16), "\n";
+echo '2^32 = 0x', gmp_strval(gmp_pow(2, 32), 16), "\n";
+echo '2^64 = 0x', gmp_strval(gmp_pow(2, 64), 16), "\n";
+echo '2^128 = 0x', gmp_strval(gmp_pow(2, 128), 16), "\n";
+echo '2^512 = 0x', gmp_strval(gmp_pow(2, 512), 16), "\n";
+echo '2^1024 = 0x', gmp_strval(gmp_pow(2, 1024), 16), "\n";
+echo '2^8192 = 0x', gmp_strval(gmp_pow(2, 8192), 16), "\n";
+?>
+--EXPECT--
+64^11 = 0x40000000000000000
+2^31 = 0x80000000
+2^32 = 0x100000000
+2^64 = 0x10000000000000000
+2^128 = 0x100000000000000000000000000000000
+2^512 = 0x100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+2^1024 = 0x10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+2^8192 = 0x100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000