diff --git a/ext/spl/tests/SplFileObject/bug20921.phpt b/ext/spl/tests/SplFileObject/bug20921.phpt
new file mode 100644
index 0000000000000..431abaf222e5d
--- /dev/null
+++ b/ext/spl/tests/SplFileObject/bug20921.phpt
@@ -0,0 +1,10 @@
+--TEST--
+Bug #20921 - Memory stream seek edge case: PHP_INT_MIN with SEEK_END
+--FILE--
+<?php
+$cls = new SplTempFileObject();
+$fusion = $cls;
+
+var_dump($fusion->fseek(PHP_INT_MIN, SEEK_END));
+--EXPECT--
+int(-1)
diff --git a/main/streams/memory.c b/main/streams/memory.c
index 2f411ff8e8c9c..37c3dc69e2280 100644
--- a/main/streams/memory.c
+++ b/main/streams/memory.c
@@ -128,7 +128,7 @@ static int php_stream_memory_seek(php_stream *stream, zend_off_t offset, int whe
 	switch(whence) {
 		case SEEK_CUR:
 			if (offset < 0) {
-				if (ms->fpos < (size_t)(-offset)) {
+				if (ms->fpos < -(size_t)offset) {
 					ms->fpos = 0;
 					*newoffs = -1;
 					return -1;
@@ -165,7 +165,7 @@ static int php_stream_memory_seek(php_stream *stream, zend_off_t offset, int whe
 				stream->eof = 0;
 				stream->fatal_error = 0;
 				return 0;
-			} else if (ZSTR_LEN(ms->data) < (size_t)(-offset)) {
+			} else if (ZSTR_LEN(ms->data) < -(size_t)offset) {
 				ms->fpos = 0;
 				*newoffs = -1;
 				return -1;