diff --git a/.changelog/5391.trivial.md b/.changelog/5391.trivial.md
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/Cargo.lock b/Cargo.lock
index 36970779d7f..5b66975a9b8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1988,8 +1988,19 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "937dd928dca340f29f67f096760ccec7853e60ebc156175aadfc8eb203eed37d"
 dependencies = [
  "impl-trait-for-tuples",
- "oasis-cbor-derive",
- "oasis-cbor-value",
+ "oasis-cbor-derive 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "oasis-cbor-value 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "thiserror",
+]
+
+[[package]]
+name = "oasis-cbor"
+version = "0.5.1"
+source = "git+https://github.com/oasisprotocol/oasis-cbor.git?branch=peternose/bugfix/skip-empty-optional-structs#95ad2e8f8c8bbd422fa958870a2d920a08ca33b9"
+dependencies = [
+ "impl-trait-for-tuples",
+ "oasis-cbor-derive 0.5.1 (git+https://github.com/oasisprotocol/oasis-cbor.git?branch=peternose/bugfix/skip-empty-optional-structs)",
+ "oasis-cbor-value 0.5.1 (git+https://github.com/oasisprotocol/oasis-cbor.git?branch=peternose/bugfix/skip-empty-optional-structs)",
  "serde",
  "thiserror",
 ]
@@ -2001,7 +2012,20 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b593c6ebad6e6429a8d1dac3509555da30311f0e6fdf93b96475bce895abef6d"
 dependencies = [
  "darling",
- "oasis-cbor-value",
+ "oasis-cbor-value 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "proc-macro-crate",
+ "proc-macro2 1.0.66",
+ "quote 1.0.33",
+ "syn 1.0.109",
+]
+
+[[package]]
+name = "oasis-cbor-derive"
+version = "0.5.1"
+source = "git+https://github.com/oasisprotocol/oasis-cbor.git?branch=peternose/bugfix/skip-empty-optional-structs#95ad2e8f8c8bbd422fa958870a2d920a08ca33b9"
+dependencies = [
+ "darling",
+ "oasis-cbor-value 0.5.1 (git+https://github.com/oasisprotocol/oasis-cbor.git?branch=peternose/bugfix/skip-empty-optional-structs)",
  "proc-macro-crate",
  "proc-macro2 1.0.66",
  "quote 1.0.33",
@@ -2014,6 +2038,11 @@ version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5fe0d7f5a7c55eba7e8e845046c6c81332f4fa4997f0ed497b9f44db1d7f2050"
 
+[[package]]
+name = "oasis-cbor-value"
+version = "0.5.1"
+source = "git+https://github.com/oasisprotocol/oasis-cbor.git?branch=peternose/bugfix/skip-empty-optional-structs#95ad2e8f8c8bbd422fa958870a2d920a08ca33b9"
+
 [[package]]
 name = "oasis-core-keymanager"
 version = "0.0.0"
@@ -2024,7 +2053,7 @@ dependencies = [
  "futures 0.3.28",
  "lazy_static",
  "lru",
- "oasis-cbor",
+ "oasis-cbor 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "oasis-core-runtime",
  "rand",
  "rustc-hex",
@@ -2067,7 +2096,7 @@ dependencies = [
  "mbedtls 0.8.3",
  "num-bigint 0.4.3",
  "num-traits",
- "oasis-cbor",
+ "oasis-cbor 0.5.1 (git+https://github.com/oasisprotocol/oasis-cbor.git?branch=peternose/bugfix/skip-empty-optional-structs)",
  "oid-registry",
  "percent-encoding",
  "rand",
@@ -2880,7 +2909,7 @@ version = "0.0.0"
 dependencies = [
  "anyhow",
  "byteorder",
- "oasis-cbor",
+ "oasis-cbor 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "oasis-core-keymanager",
  "oasis-core-runtime",
  "oasis-core-tools",
diff --git a/keymanager/Cargo.toml b/keymanager/Cargo.toml
index 245e2eb5811..5574f1b4deb 100644
--- a/keymanager/Cargo.toml
+++ b/keymanager/Cargo.toml
@@ -6,6 +6,7 @@ edition = "2018"
 
 [dependencies]
 oasis-core-runtime = { path = "../runtime" }
+# TODO: Upgrade.
 cbor = { version = "0.5.1", package = "oasis-cbor" }
 
 # Third party.
diff --git a/runtime/Cargo.toml b/runtime/Cargo.toml
index e154b7652b3..8d31292e874 100644
--- a/runtime/Cargo.toml
+++ b/runtime/Cargo.toml
@@ -5,7 +5,10 @@ authors = ["Oasis Protocol Foundation <info@oasisprotocol.org>"]
 edition = "2018"
 
 [dependencies]
-cbor = { version = "0.5.1", package = "oasis-cbor", features = ["serde"] }
+# TODO: Upgrade.
+cbor = { package = "oasis-cbor", features = [
+    "serde",
+], git = 'https://github.com/oasisprotocol/oasis-cbor.git', branch = 'peternose/bugfix/skip-empty-optional-structs' }
 
 # Third party.
 log = "0.4"
@@ -35,7 +38,9 @@ futures = "0.3.25"
 tokio = { version = "1.29.1", features = ["rt", "rt-multi-thread", "sync"] }
 tendermint = "0.30.0"
 tendermint-proto = "0.30.0"
-tendermint-light-client = { version = "0.30.0", features = ["rust-crypto"], default-features = false }
+tendermint-light-client = { version = "0.30.0", features = [
+    "rust-crypto",
+], default-features = false }
 tendermint-rpc = { version = "0.30.0", default-features = false }
 curve25519-dalek = { version = "4.0.0", features = ["legacy_compatibility"] }
 x25519-dalek = { version = "2.0.0", features = ["static_secrets"] }
diff --git a/runtime/src/consensus/registry.rs b/runtime/src/consensus/registry.rs
index 301127a54d7..cbe57c96d79 100644
--- a/runtime/src/consensus/registry.rs
+++ b/runtime/src/consensus/registry.rs
@@ -752,11 +752,9 @@ mod tests {
     fn test_consistent_runtime() {
         // NOTE: These tests MUST be synced with go/registry/api/runtime.go.
         let tcs = vec![
-            // FIXME: Change to "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" once cbor is fixed.
-            ("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", Runtime::default()),
-            // FIXME: Change to "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" once cbor is fixed.
+            ("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", Runtime::default()),
             (
-                "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",
+                "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",
                 Runtime {
                     staking: RuntimeStakingParameters {
                         thresholds: BTreeMap::new(),
@@ -768,9 +766,8 @@ mod tests {
                     ..Default::default()
                 },
             ),
-            // FIXME: Change to "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" once cbor is fixed.
             (
-                "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",
+                "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",
                 Runtime {
                     staking: RuntimeStakingParameters {
                         thresholds: BTreeMap::new(),
diff --git a/runtime/src/consensus/roothash/message.rs b/runtime/src/consensus/roothash/message.rs
index 82fbe3f367f..d4e377a24d3 100644
--- a/runtime/src/consensus/roothash/message.rs
+++ b/runtime/src/consensus/roothash/message.rs
@@ -306,8 +306,7 @@ mod tests {
                     0,
                     RegistryMessage::UpdateRuntime(registry::Runtime::default()),
                 ))],
-                // FIXME: Change to e6e170fb771583147255e0c96dc88615d4fd2fd28488ae489df01da201affe72 once cbor is fixed.
-                "baf9eeaa4860e363a9c27d99555839afc535f0cd32d23dc640f0f020677460e0",
+                "e6e170fb771583147255e0c96dc88615d4fd2fd28488ae489df01da201affe72",
             ),
             (
                 vec![Message::Registry(Versioned::new(
diff --git a/tests/runtimes/simple-keyvalue/Cargo.toml b/tests/runtimes/simple-keyvalue/Cargo.toml
index 0a97279d9db..70f1e2d788a 100644
--- a/tests/runtimes/simple-keyvalue/Cargo.toml
+++ b/tests/runtimes/simple-keyvalue/Cargo.toml
@@ -20,6 +20,7 @@ stack-size = 2097152
 threads = 8
 
 [dependencies]
+# TODO: Upgrade.
 cbor = { version = "0.5.1", package = "oasis-cbor" }
 oasis-core-runtime = { path = "../../../runtime" }
 oasis-core-keymanager = { path = "../../../keymanager" }