diff --git a/ext/standard/string.c b/ext/standard/string.c
index 4f255d4d8e9..09d68c11237 100644
--- a/ext/standard/string.c
+++ b/ext/standard/string.c
@@ -5770,6 +5770,10 @@ PHP_FUNCTION(substr_compare)
 		RETURN_FALSE;
 	}
 
+	if (offset < 0) { /* negative offset, start comparison at the end of string */
+		offset = s1_len + offset;
+	}
+
 	if (len && offset >= s1_len) {
 		php_error_docref(NULL TSRMLS_CC, E_WARNING, "The start position cannot exceed initial string length.");
 		RETURN_FALSE;