diff --git a/contrib/test.sh b/contrib/test.sh
index e308ce3c..2aa5a279 100755
--- a/contrib/test.sh
+++ b/contrib/test.sh
@@ -16,7 +16,10 @@ fi
 # Test pinned versions.
 if cargo --version | grep ${MSRV}; then
     cargo update -p tempfile --precise 3.3.0
+    cargo update -p cc --precise 1.0.79
     cargo update -p log --precise 0.4.18
+    cargo update -p serde_json --precise 1.0.96
+    cargo update -p serde --precise 1.0.156
 fi
 
 # Integration test.
diff --git a/json/Cargo.toml b/json/Cargo.toml
index 8f3d67cc..c4006e9b 100644
--- a/json/Cargo.toml
+++ b/json/Cargo.toml
@@ -23,4 +23,4 @@ path = "src/lib.rs"
 serde = { version = "1", features = [ "derive" ] }
 serde_json = "1"
 
-bitcoin = { version = "0.31.0", features = ["serde", "rand-std"]}
+bitcoin = { version = "0.31.0", features = ["serde", "rand-std", "base64"]}