diff --git a/db/Cargo.toml b/db/Cargo.toml
index a356fb2c..f89121b7 100644
--- a/db/Cargo.toml
+++ b/db/Cargo.toml
@@ -14,7 +14,6 @@ indexmap = "1"
 itertools = "0.7"
 lazy_static = "0.2"
 log = "0.4"
-num = "0.1"
 ordered-float = "0.5"
 time = "0.1"
 petgraph = "0.4.12"
diff --git a/db/src/cache.rs b/db/src/cache.rs
index 144e746d..ef1a7bb4 100644
--- a/db/src/cache.rs
+++ b/db/src/cache.rs
@@ -76,8 +76,6 @@ use failure::{
     ResultExt,
 };
 
-use num;
-
 use rusqlite;
 
 use mentat_core::{
@@ -128,17 +126,10 @@ trait Remove<T> where T: PartialEq {
 
 impl<T> Remove<T> for Vec<T> where T: PartialEq {
     /// Remove all occurrences from a vector in-place, by equality.
-    /// Eventually replace with unstable feature: #40062.
     fn remove_every(&mut self, item: &T) -> usize {
-        let mut removed = 0;
-        let range = num::range_step_inclusive(self.len() as isize - 1, 0, -1);
-        for i in range {
-            if self.get(i as usize).map_or(false, |x| x == item) {
-                self.remove(i as usize);
-                removed += 1;
-            }
-        }
-        removed
+        let initial_len = self.len();
+        self.retain(|v| v != item);
+        initial_len - self.len()
     }
 }
 
@@ -187,10 +178,14 @@ impl<K, V> ExtendByAbsorbing for BTreeMap<K, V> where K: Ord, V: Absorb {
 #[test]
 fn test_vec_remove_item() {
     let mut v = vec![1, 2, 3, 4, 5, 4, 3];
-    v.remove_every(&3);
+    let count = v.remove_every(&3);
     assert_eq!(v, vec![1, 2, 4, 5, 4]);
-    v.remove_every(&4);
+    assert_eq!(count, 2);
+    let count = v.remove_every(&4);
     assert_eq!(v, vec![1, 2, 5]);
+    assert_eq!(count, 2);
+    let count = v.remove_every(&9);
+    assert_eq!(count, 0);
 }
 
 //
diff --git a/db/src/lib.rs b/db/src/lib.rs
index bd8fe154..c42b8eaf 100644
--- a/db/src/lib.rs
+++ b/db/src/lib.rs
@@ -15,7 +15,6 @@ extern crate itertools;
 #[macro_use] extern crate lazy_static;
 #[macro_use] extern crate log;
 
-extern crate num;
 extern crate petgraph;
 extern crate rusqlite;
 extern crate tabwriter;