diff --git a/Cargo.toml b/Cargo.toml
index aecf7777..155de55f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -30,7 +30,7 @@ net2 = "0.2.16"
 rustc-serialize = { version = "0.3", optional = true }
 chrono = { version = "0.2.14", optional = true }
 openssl = { version = ">= 0.6.4, < 0.8", optional = true }
-serde_json = { version = "0.6", optional = true }
+serde_json = { version = ">= 0.6, < 0.8", optional = true }
 time = { version = "0.1.14", optional = true }
 unix_socket = { version = "0.5", optional = true }
 uuid = { version = "0.1", optional = true }