diff --git a/packages/sandbox/src/compilerOptions.ts b/packages/sandbox/src/compilerOptions.ts
index ec202423c15f..353b1d9fe2ae 100644
--- a/packages/sandbox/src/compilerOptions.ts
+++ b/packages/sandbox/src/compilerOptions.ts
@@ -10,6 +10,8 @@ type Monaco = typeof import("monaco-editor")
 export function getDefaultSandboxCompilerOptions(config: SandboxConfig, monaco: Monaco) {
   const useJavaScript = config.filetype === "js"
   const settings: CompilerOptions = {
+    strict: true,
+
     noImplicitAny: true,
     strictNullChecks: !useJavaScript,
     strictFunctionTypes: true,
@@ -60,24 +62,40 @@ export function getDefaultSandboxCompilerOptions(config: SandboxConfig, monaco:
  * Loop through all of the entries in the existing compiler options then compare them with the
  * query params and return an object which is the changed settings via the query params
  */
-export const getCompilerOptionsFromParams = (options: CompilerOptions, params: URLSearchParams): CompilerOptions => {
-  const urlDefaults = Object.entries(options).reduce((acc: any, [key, value]) => {
-    if (params.has(key)) {
-      const urlValue = params.get(key)!
-
-      if (urlValue === "true") {
-        acc[key] = true
-      } else if (urlValue === "false") {
-        acc[key] = false
-      } else if (!isNaN(parseInt(urlValue, 10))) {
-        acc[key] = parseInt(urlValue, 10)
+export const getCompilerOptionsFromParams = (
+  playgroundDefaults: CompilerOptions,
+  ts: typeof import("typescript"),
+  params: URLSearchParams
+): CompilerOptions => {
+  const returnedOptions: CompilerOptions = {}
+
+  params.forEach((val, key) => {
+    // First use the defaults object to drop compiler flags which are already set to the default
+    if (playgroundDefaults[key]) {
+      let toSet = undefined
+      if (val === "true" && playgroundDefaults[key] !== true) {
+        toSet = true
+      } else if (val === "false" && playgroundDefaults[key] !== false) {
+        toSet = false
+      } else if (!isNaN(parseInt(val, 10)) && playgroundDefaults[key] !== parseInt(val, 10)) {
+        toSet = parseInt(val, 10)
       }
-    }
 
-    return acc
-  }, {})
+      if (toSet !== undefined) returnedOptions[key] = toSet
+    } else {
+      // If that doesn't work, double check that the flag exists and allow it through
+      // @ts-ignore
+      const flagExists = ts.optionDeclarations.find(opt => opt.name === key)
+      if (flagExists) {
+        let realValue: number | boolean = true
+        if (val === "false") realValue = false
+        if (!isNaN(parseInt(val, 10))) realValue = parseInt(val, 10)
+        returnedOptions[key] = realValue
+      }
+    }
+  })
 
-  return urlDefaults
+  return returnedOptions
 }
 
 // Can't set sandbox to be the right type because the param would contain this function
diff --git a/packages/sandbox/src/index.ts b/packages/sandbox/src/index.ts
index 5117a00cb90d..0723b71081aa 100644
--- a/packages/sandbox/src/index.ts
+++ b/packages/sandbox/src/index.ts
@@ -123,7 +123,7 @@ export const createTypeScriptSandbox = (
   let compilerOptions: CompilerOptions
   if (!config.suppressAutomaticallyGettingCompilerFlags) {
     const params = new URLSearchParams(location.search)
-    let queryParamCompilerOptions = getCompilerOptionsFromParams(compilerDefaults, params)
+    let queryParamCompilerOptions = getCompilerOptionsFromParams(compilerDefaults, ts, params)
     if (Object.keys(queryParamCompilerOptions).length)
       config.logger.log("[Compiler] Found compiler options in query params: ", queryParamCompilerOptions)
     compilerOptions = { ...compilerDefaults, ...queryParamCompilerOptions }
diff --git a/packages/sandbox/test/defaultCompilerOptions.test.ts b/packages/sandbox/test/defaultCompilerOptions.test.ts
new file mode 100644
index 000000000000..c4cf6201479e
--- /dev/null
+++ b/packages/sandbox/test/defaultCompilerOptions.test.ts
@@ -0,0 +1,59 @@
+import { getCompilerOptionsFromParams, getDefaultSandboxCompilerOptions } from "../src/compilerOptions"
+import ts from "typescript"
+
+const fauxMonaco: any = {
+  languages: {
+    typescript: {
+      ModuleResolutionKind: ts.ModuleResolutionKind,
+      ScriptTarget: ts.ScriptTarget,
+      JsxEmit: ts.JsxEmit,
+      ModuleKind: ts.ModuleKind,
+    },
+  },
+}
+
+describe(getCompilerOptionsFromParams, () => {
+  it("ignores compiler flags which are the same as the defaults", () => {
+    // noImplicitReturns=true is the default, and shouldnt be in the object
+    const params = new URLSearchParams("?noImplicitThis=false&noImplicitReturns=true#code/JYOw")
+    const defaults = getDefaultSandboxCompilerOptions({ filetype: "js" } as any, fauxMonaco)
+
+    expect(getCompilerOptionsFromParams(defaults, ts, params)).toMatchInlineSnapshot(`
+      Object {
+        "noImplicitThis": false,
+      }
+    `)
+  })
+
+  it("ignores non-compiler flags", () => {
+    const params = new URLSearchParams("?asdasdasdasd=false")
+    const defaults = getDefaultSandboxCompilerOptions({ filetype: "js" } as any, fauxMonaco)
+
+    expect(getCompilerOptionsFromParams(defaults, ts, params)).toMatchInlineSnapshot(`Object {}`)
+  })
+
+  it("handles mapped types like target et", () => {
+    const params = new URLSearchParams("?target=6")
+    const defaults = getDefaultSandboxCompilerOptions({ filetype: "js" } as any, fauxMonaco)
+
+    expect(getCompilerOptionsFromParams(defaults, ts, params)).toMatchInlineSnapshot(`
+      Object {
+        "target": 6,
+      }
+    `)
+  })
+
+  it("handles settings options which haven't been given defaults in the monaco defaults", () => {
+    const search = "?ts=4.4.0-beta&exactOptionalPropertyTypes=true#code/JYOw"
+    const params = new URLSearchParams(search)
+    expect(params.has("exactOptionalPropertyTypes")).toBeTruthy()
+
+    const defaults = getDefaultSandboxCompilerOptions({ filetype: "js" } as any, fauxMonaco)
+
+    expect(getCompilerOptionsFromParams(defaults, ts, params)).toMatchInlineSnapshot(`
+      Object {
+        "exactOptionalPropertyTypes": true,
+      }
+    `)
+  })
+})