diff --git a/bigint/Cargo.toml b/bigint/Cargo.toml
index 6708bcf..2c01cc3 100644
--- a/bigint/Cargo.toml
+++ b/bigint/Cargo.toml
@@ -29,7 +29,7 @@ version = "0.3.19"
 
 [dependencies.serde]
 optional = true
-version = "0.7.0"
+version = ">= 0.7.0, < 0.9.0"
 
 [features]
 default = ["rand", "rustc-serialize"]
diff --git a/complex/Cargo.toml b/complex/Cargo.toml
index 9927cf4..4687574 100644
--- a/complex/Cargo.toml
+++ b/complex/Cargo.toml
@@ -22,7 +22,7 @@ version = "0.3.19"
 
 [dependencies.serde]
 optional = true
-version = "^0.7.0"
+version = ">= 0.7.0, < 0.9.0"
 
 [features]
 default = ["rustc-serialize"]
diff --git a/rational/Cargo.toml b/rational/Cargo.toml
index c2f0c60..67621e5 100644
--- a/rational/Cargo.toml
+++ b/rational/Cargo.toml
@@ -30,7 +30,7 @@ version = "0.3.19"
 
 [dependencies.serde]
 optional = true
-version = "0.7.0"
+version = ">= 0.7.0, < 0.9.0"
 
 [features]
 default = ["bigint", "rustc-serialize"]