diff --git a/pysubs2/formats/jsonformat.py b/pysubs2/formats/jsonformat.py
index 85f37c7..2f9acc5 100644
--- a/pysubs2/formats/jsonformat.py
+++ b/pysubs2/formats/jsonformat.py
@@ -27,7 +27,7 @@ class JSONFormat(FormatBase):
     @classmethod
     def guess_format(cls, text: str) -> Optional[str]:
         """See :meth:`pysubs2.formats.FormatBase.guess_format()`"""
-        if text.startswith("{\"") and "\"info:\"" in text:
+        if text.startswith("{\"") and "\"info\":" in text:
             return "json"
         else:
             return None
diff --git a/tests/formats/test_json.py b/tests/formats/test_json.py
index 26a6b1d..094d112 100644
--- a/tests/formats/test_json.py
+++ b/tests/formats/test_json.py
@@ -17,8 +17,10 @@ def test_write_read() -> None:
     json_text = subs.to_string("json")
 
     subs2 = SSAFile.from_string(json_text, "json")
+    subs3 = SSAFile.from_string(json_text)
 
     assert subs2.equals(subs)
+    assert subs3.equals(subs)
 
 
 def test_read_unsupported_json_issue_85() -> None: