diff --git a/ext/standard/image.c b/ext/standard/image.c
index 15761364c341..0e6ee0897975 100644
--- a/ext/standard/image.c
+++ b/ext/standard/image.c
@@ -874,7 +874,7 @@ static struct gfxinfo *php_handle_iff(php_stream * stream)
 		if (size < 0) {
 			return NULL;
 		}
-		if ((size & 1) == 1) {
+		if ((size & 1) == 1 && size < INT_MAX) {
 			size++;
 		}
 		if (chunkId == 0x424d4844) { /* BMHD chunk */
diff --git a/ext/standard/tests/image/getimagesizefromstring_iff_overflow.phpt b/ext/standard/tests/image/getimagesizefromstring_iff_overflow.phpt
new file mode 100644
index 000000000000..ed8f8d4b901b
--- /dev/null
+++ b/ext/standard/tests/image/getimagesizefromstring_iff_overflow.phpt
@@ -0,0 +1,14 @@
+--TEST--
+getimagesizefromstring() IFF chunk size integer overflow (GH-getimagesize_oflow)
+--CREDITS--
+Alexandre Daubois
+--FILE--
+<?php
+// IFF/ILBM with a chunk size of INT_MAX (0x7fffffff), an odd value.
+// The parser rounds odd chunk sizes up to even via size++, which overflowed
+// when size == INT_MAX. It must be handled gracefully rather than triggering UB.
+$payload = "FORM" . "\x00\x00\x00\x00" . "ILBM" . "ABCD" . "\x7f\xff\xff\xff";
+var_dump(getimagesizefromstring($payload));
+?>
+--EXPECT--
+bool(false)