diff --git a/src/browser/browserSpecUtils.ts b/src/browser/browserSpecUtils.ts
index ba75e486..7ca324dc 100644
--- a/src/browser/browserSpecUtils.ts
+++ b/src/browser/browserSpecUtils.ts
@@ -33,7 +33,7 @@ export const consoleHandler = (message: puppeteer.ConsoleMessage) => {
         case 'trace': console.trace(text); break // tslint:disable-line:no-console
         case 'assert': console.assert(text); break // tslint:disable-line:no-console
         case 'profile': console.profile(text); break // tslint:disable-line:no-console
-        case 'profileEnd': console.profileEnd(text); break // tslint:disable-line:no-console
+        case 'profileEnd': console.profileEnd(); break // tslint:disable-line:no-console
         case 'count': console.count(text); break // tslint:disable-line:no-console
         case 'timeEnd': console.timeEnd(text); break // tslint:disable-line:no-console
 
diff --git a/src/models/rule.ts b/src/models/rule.ts
index cf655f89..24ec667b 100644
--- a/src/models/rule.ts
+++ b/src/models/rule.ts
@@ -1891,7 +1891,7 @@ export class SimpleNeighbor extends BaseForLines implements ICacheable {
 
         let didChangeSprites = false
         let didChangeDirection = false
-        const orTilesRemoved = new Set()
+        const orTilesRemoved = new Set<IGameTile>()
         let allMessages: Array<A11Y_MESSAGE<Cell, GameSprite>> = []
         for (const replaceTile of replaceTiles) {
             const { didActuallyChange, messages } = replaceTile.replace(cell, magicOrTiles, orTilesRemoved)
diff --git a/src/models/tile.ts b/src/models/tile.ts
index 3b7cb83c..c92309f7 100644
--- a/src/models/tile.ts
+++ b/src/models/tile.ts
@@ -105,7 +105,7 @@ export abstract class GameSprite extends BaseForLines implements IGameTile {
         return cell.getSpritesAsSet().has(this)
         // because of Webworkers, we cannot perform equality tests (unless the sprites match exactly what comes out of gamedata... hmm, maybe that's the way to do it?)
     }
-    public getSpritesThatMatch(cell: Cellish) {
+    public getSpritesThatMatch(cell: Cellish): Set<GameSprite> {
         if (cell.getSpritesAsSet().has(this)) {
             return new Set([this])
         } else {
@@ -187,7 +187,7 @@ export abstract class GameSprite extends BaseForLines implements IGameTile {
         }
         return false
     }
-    public getCellsThatMatch<T extends Cellish>(cells?: Iterable<T>) {
+    public getCellsThatMatch<T extends Cellish>(cells?: Iterable<T>): Set<T> {
         if (this.trickleCells.size > 0) {
             return (this.trickleCells as unknown) as Set<T>
         } else if (cells) {
@@ -345,15 +345,15 @@ export abstract class GameLegendTile extends BaseForLines implements IGameTile {
         return firstCollisionLayer
     }
     public getCollisionLayers() {
-        const layers = new Set()
+        const layers = new Set<CollisionLayer>()
         for (const sprite of this.getSprites()) {
             layers.add(sprite.getCollisionLayer())
         }
         return [...layers]
     }
 
-    public getCellsThatMatch(cells?: Iterable<Cellish>) {
-        const matches = new Set()
+    public getCellsThatMatch<T extends Cellish>(cells?: Iterable<T>): Set<T> {
+        const matches = new Set<T>()
         for (const sprite of this.getSprites()) {
             for (const cell of sprite.getCellsThatMatch(cells)) {
                 matches.add(cell)
@@ -448,7 +448,7 @@ export class GameLegendTileSimple extends GameLegendTile {
         return true
     }
 
-    public getSpritesThatMatch(cell: Cellish) {
+    public getSpritesThatMatch(cell: Cellish): Set<GameSprite> {
         return setIntersection(new Set(this.getSprites()), cell.getSpritesAsSet())
     }
 
diff --git a/src/sortedList.ts b/src/sortedList.ts
index dab2f790..7bc71c53 100644
--- a/src/sortedList.ts
+++ b/src/sortedList.ts
@@ -59,7 +59,7 @@ class ListItem<T> {
     }
 }
 
-class IteratorResultDone<T> implements IteratorResult<T> {
+class IteratorResultDone<T> implements IteratorReturnResult<T> {
     public done: true
     public value: T
     constructor() {
@@ -67,7 +67,7 @@ class IteratorResultDone<T> implements IteratorResult<T> {
         this.value = {} as T // tslint:disable-line:no-object-literal-type-assertion
     }
 }
-class ListIteratorResult<T> implements IteratorResult<T> {
+class ListIteratorResult<T> implements IteratorYieldResult<T> {
     public value: T
     public done: false
     constructor(value: T) {
diff --git a/src/util.ts b/src/util.ts
index 7a025805..e772adcc 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -118,7 +118,7 @@ export function setAddAll<T>(setA: Set<T>, iterable: Iterable<T>) {
 }
 
 export function setIntersection<T>(setA: Set<T>, setB: Iterable<T>) {
-    const intersection = new Set()
+    const intersection = new Set<T>()
     for (const elem of setB) {
         if (setA.has(elem)) {
             intersection.add(elem)
diff --git a/yarn.lock b/yarn.lock
index 243de4a2..704996e4 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -8861,11 +8861,16 @@ typedoc@^0.14.0:
     typedoc-default-themes "^0.5.0"
     typescript "3.2.x"
 
-typescript@3.2.x, typescript@^3.2.2:
+typescript@3.2.x:
   version "3.2.2"
   resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.2.2.tgz#fe8101c46aa123f8353523ebdcf5730c2ae493e5"
   integrity sha512-VCj5UiSyHBjwfYacmDuc/NOk4QQixbE+Wn7MFJuS0nRuPQbof132Pw4u53dm264O8LPc2MVsc7RJNml5szurkg==
 
+typescript@^3.2.2:
+  version "3.9.7"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.9.7.tgz#98d600a5ebdc38f40cb277522f12dc800e9e25fa"
+  integrity sha512-BLbiRkiBzAwsjut4x/dsibSTB6yWpwT5qWmC2OfuCg3GgVQCSgMs4vEctYPhsaGtd0AeuuHMkjZ2h2WG8MSzRw==
+
 uglify-js@3.4.x:
   version "3.4.9"
   resolved "https://registry.yarnpkg.com/uglify-js/-/uglify-js-3.4.9.tgz#af02f180c1207d76432e473ed24a28f4a782bae3"