diff --git a/Cargo.lock b/Cargo.lock
index 4ebb7751c44..32636cc20d7 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -167,7 +167,7 @@ dependencies = [
  "chalk-ir 0.1.0",
  "chalk-macros 0.1.0",
  "chalk-parse 0.1.0",
- "ena 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ena 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -222,12 +222,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "ena"
-version = "0.4.0"
+version = "0.9.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "log 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
 
 [[package]]
 name = "ena"
-version = "0.9.3"
+version = "0.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "log 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -794,7 +797,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum docopt 0.8.3 (registry+https://github.com/rust-lang/crates.io-index)" = "d8acd393692c503b168471874953a2531df0e9ab77d0b6bbc582395743300a4a"
 "checksum docopt 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "d60c92df70dfaaabecc14b409fd79f55ba0f247780529db1d73bfa601e1d3ac0"
 "checksum either 1.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3be565ca5c557d7f59e7cfcf1844f9e3033650c929c6566f511e8005f205c1d0"
-"checksum ena 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5c109645f12ca057044ef2ffa56670cf7e3fd1fa530d73cd185e8298b03380b5"
+"checksum ena 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)" = "25b4e5febb25f08c49f1b07dc33a182729a6b21edfb562b5aef95f78e0dbe5bb"
 "checksum ena 0.9.3 (registry+https://github.com/rust-lang/crates.io-index)" = "88dc8393b3c7352f94092497f6b52019643e493b6b890eb417cdb7c46117e621"
 "checksum encode_unicode 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "28d65f1f5841ef7c6792861294b72beda34c664deb8be27970f36c306b7da1ce"
 "checksum error-chain 0.12.0 (registry+https://github.com/rust-lang/crates.io-index)" = "07e791d3be96241c77c43846b665ef1384606da2cd2a48730abe606a12906e02"
diff --git a/chalk-solve/Cargo.toml b/chalk-solve/Cargo.toml
index 5a652624e35..18e9ca2a330 100644
--- a/chalk-solve/Cargo.toml
+++ b/chalk-solve/Cargo.toml
@@ -9,7 +9,7 @@ readme = "README.md"
 keywords = ["compiler", "traits", "prolog"]
 
 [dependencies]
-ena = "0.4"
+ena = "0.10.1"
 
 [dependencies.chalk-macros]
 version = "0.1.0"
diff --git a/chalk-solve/src/infer.rs b/chalk-solve/src/infer.rs
index e0b2e74959d..ccb9386eff4 100644
--- a/chalk-solve/src/infer.rs
+++ b/chalk-solve/src/infer.rs
@@ -15,13 +15,13 @@ use self::var::*;
 
 #[derive(Clone)]
 pub struct InferenceTable {
-    unify: ena::UnificationTable<EnaVariable>,
+    unify: ena::InPlaceUnificationTable<EnaVariable>,
     vars: Vec<EnaVariable>,
     max_universe: UniverseIndex,
 }
 
 pub struct InferenceSnapshot {
-    unify_snapshot: ena::Snapshot<EnaVariable>,
+    unify_snapshot: ena::Snapshot<ena::InPlace<EnaVariable>>,
     max_universe: UniverseIndex,
     vars: Vec<EnaVariable>,
 }
diff --git a/chalk-solve/src/infer/var.rs b/chalk-solve/src/infer/var.rs
index d202b0e108a..676b4f99dcf 100644
--- a/chalk-solve/src/infer/var.rs
+++ b/chalk-solve/src/infer/var.rs
@@ -95,6 +95,8 @@ impl From<Lifetime> for InferenceValue {
 }
 
 impl UnifyValue for InferenceValue {
+    type Error = (InferenceValue, InferenceValue);
+
     fn unify_values(
         a: &InferenceValue,
         b: &InferenceValue,