diff --git a/main/streams/memory.c b/main/streams/memory.c
index 2f411ff8e8c9c..e6969e2038e3e 100644
--- a/main/streams/memory.c
+++ b/main/streams/memory.c
@@ -125,6 +125,11 @@ static int php_stream_memory_seek(php_stream *stream, zend_off_t offset, int whe
 	php_stream_memory_data *ms = (php_stream_memory_data*)stream->abstract;
 	assert(ms != NULL);
 
+	if (offset == ZEND_LONG_MIN) {
+		zend_argument_value_error(2, "must be greater than " ZEND_LONG_FMT, ZEND_LONG_MIN);
+		return FAILURE;
+	}
+
 	switch(whence) {
 		case SEEK_CUR:
 			if (offset < 0) {
diff --git a/tests/basic/bug20964.phpt b/tests/basic/bug20964.phpt
new file mode 100644
index 0000000000000..9aae8946818ec
--- /dev/null
+++ b/tests/basic/bug20964.phpt
@@ -0,0 +1,15 @@
+--TEST--
+Bug #20964 fseek with PHP_INT_MIN on php://memory
+--FILE--
+<?php
+$stream = fopen('php://memory', 'r+');
+
+$result = fseek($stream, PHP_INT_MIN, SEEK_END);
+var_dump($result);
+?>
+--EXPECTF--
+Fatal error: Uncaught ValueError: fseek(): Argument #2 ($offset) must be greater than -%d in %s:%d
+Stack trace:
+#0 %s(%d): fseek(Resource id #%d, -%d, %d)
+#1 {main}
+  thrown in %s on line %d
\ No newline at end of file