diff --git a/pdfminer/psparser.py b/pdfminer/psparser.py
index d74c7477..aa9b2d86 100755
--- a/pdfminer/psparser.py
+++ b/pdfminer/psparser.py
@@ -607,7 +607,7 @@ def _parse_hexstring(self) -> bytes:
 )
 STRLEXER = re.compile(
     rb"""(?:
-      (?P<octal> \\\d{1,3})
+      (?P<octal> \\[0-7]{1,3})
     | (?P<linebreak> \\(?:\r\n?|\n))
     | (?P<escape> \\.)
     | (?P<parenleft> \()