diff --git a/oauth2/__init__.py b/oauth2/__init__.py
index 835270e3..36b65612 100644
--- a/oauth2/__init__.py
+++ b/oauth2/__init__.py
@@ -284,7 +284,7 @@ def from_string(s):
         if not len(s):
             raise ValueError("Invalid parameter string.")
 
-        params = parse_qs(s, keep_blank_values=False)
+        params = parse_qs(s, keep_blank_values=True)
         if not len(params):
             raise ValueError("Invalid parameter string.")