diff --git a/types/dompurify/dompurify-tests.ts b/types/dompurify/dompurify-tests.ts
index 263368f20e..356225b7c3 100644
--- a/types/dompurify/dompurify-tests.ts
+++ b/types/dompurify/dompurify-tests.ts
@@ -3,56 +3,60 @@
 import dompurify = require('dompurify');
 
 dompurify.sanitize('<script>alert("hi")</script>');
-dompurify.addHook('beforeSanitizeElements', (el, data, config) => {
-    return el;
-});
+dompurify.addHook('beforeSanitizeElements', (el, data, config) => undefined);
 
 //examples from the DOMPurify README
 let dirty = '<script>alert("hi")</script><p>Totally safe<p><p onerror="blowUp()">Totally not safe</p>';
+let str: string;
+let elem: HTMLElement;
+let frag: DocumentFragment;
 
 // allow only <b>
-dompurify.sanitize(dirty, { ALLOWED_TAGS: ['b'] });
+str = dompurify.sanitize(dirty, { ALLOWED_TAGS: ['b'] });
 
 // allow only <b> and <q> with style attributes (for whatever reason)
-dompurify.sanitize(dirty, { ALLOWED_TAGS: ['b', 'q'], ALLOWED_ATTR: ['style'] });
+str = dompurify.sanitize(dirty, { ALLOWED_TAGS: ['b', 'q'], ALLOWED_ATTR: ['style'] });
 
 // leave all as it is but forbid <style>
-dompurify.sanitize(dirty, { FORBID_TAGS: ['style'] });
+str = dompurify.sanitize(dirty, { FORBID_TAGS: ['style'] });
 
 // leave all as it is but forbid style attributes
-dompurify.sanitize(dirty, { FORBID_ATTR: ['style'] });
+str = dompurify.sanitize(dirty, { FORBID_ATTR: ['style'] });
 
 // extend the existing array of allowed tags
-dompurify.sanitize(dirty, { ADD_TAGS: ['my-tag'] });
+str = dompurify.sanitize(dirty, { ADD_TAGS: ['my-tag'] });
 
 // extend the existing array of attributes
-dompurify.sanitize(dirty, { ADD_ATTR: ['my-attr'] });
+str = dompurify.sanitize(dirty, { ADD_ATTR: ['my-attr'] });
 
 // prohibit HTML5 data attributes (default is true)
-dompurify.sanitize(dirty, { ALLOW_DATA_ATTR: false });
+str = dompurify.sanitize(dirty, { ALLOW_DATA_ATTR: false });
 
 // return a DOM HTMLBodyElement instead of an HTML string (default is false)
-dompurify.sanitize(dirty, { RETURN_DOM: true }) as HTMLElement;
+str = dompurify.sanitize(dirty, { RETURN_DOM: false });
+elem = dompurify.sanitize(dirty, { RETURN_DOM: true });
+elem = dompurify.sanitize(dirty, { RETURN_DOM: true, RETURN_DOM_FRAGMENT: false });
 
 // return a DOM DocumentFragment instead of an HTML string (default is false)
-dompurify.sanitize(dirty, { RETURN_DOM_FRAGMENT: true }) as DocumentFragment;
-dompurify.sanitize(dirty, { RETURN_DOM_FRAGMENT: true, RETURN_DOM: true }) as DocumentFragment;
+str = dompurify.sanitize(dirty, { RETURN_DOM_FRAGMENT: false });
+frag = dompurify.sanitize(dirty, { RETURN_DOM_FRAGMENT: true });
+frag = dompurify.sanitize(dirty, { RETURN_DOM_FRAGMENT: true, RETURN_DOM: false });
+frag = dompurify.sanitize(dirty, { RETURN_DOM_FRAGMENT: true, RETURN_DOM: true });
 
 // return a DOM DocumentFragment instead of an HTML string (default is false)
 // also import it into the current document (default is false).
 // RETURN_DOM_IMPORT must be set if you would like to append
 // the returned node to the current document
-let clean = dompurify.sanitize(dirty, { RETURN_DOM_FRAGMENT: true, RETURN_DOM_IMPORT: true });
-document.body.appendChild(clean);
+frag = dompurify.sanitize(dirty, { RETURN_DOM_FRAGMENT: true, RETURN_DOM_IMPORT: true });
 
 // return entire document including <html> tags (default is false)
-dompurify.sanitize(dirty, { WHOLE_DOCUMENT: true });
+str = dompurify.sanitize(dirty, { WHOLE_DOCUMENT: true });
 
 // make output safe for usage in jQuery's $()/html() method (default is false)
-dompurify.sanitize(dirty, { SAFE_FOR_JQUERY: true });
+str = dompurify.sanitize(dirty, { SAFE_FOR_JQUERY: true });
 
 // disable DOM Clobbering protection on output (default is true, handle with care!)
-dompurify.sanitize(dirty, { SANITIZE_DOM: false });
+str = dompurify.sanitize(dirty, { SANITIZE_DOM: false });
 
 // discard an element's content when the element is removed (default is true)
-dompurify.sanitize(dirty, { KEEP_CONTENT: false });
+str = dompurify.sanitize(dirty, { KEEP_CONTENT: false });
diff --git a/types/dompurify/index.d.ts b/types/dompurify/index.d.ts
index 43e0a016c7..5406156bca 100644
--- a/types/dompurify/index.d.ts
+++ b/types/dompurify/index.d.ts
@@ -10,9 +10,10 @@ declare var DOMPurify: DOMPurify;
 
 interface DOMPurify {
     sanitize(source: string | Node): string;
+    sanitize(source: string | Node, config: DOMPurifyConfig & { RETURN_DOM_FRAGMENT?: false; RETURN_DOM?: false; }): string;
     sanitize(source: string | Node, config: DOMPurifyConfig & { RETURN_DOM_FRAGMENT: true; }): DocumentFragment;
     sanitize(source: string | Node, config: DOMPurifyConfig & { RETURN_DOM: true; }): HTMLElement;
-    sanitize<T extends string | HTMLElement | DocumentFragment>(source: string | Node, config: DOMPurifyConfig): T;
+    sanitize(source: string | Node, config: DOMPurifyConfig): string | HTMLElement | DocumentFragment;
     addHook(hook: 'uponSanitizeElement', cb: (currentNode: Element, data: DOMPurifySanitizeElementHookEvent, config: DOMPurifyConfig) => void): void;
     addHook(hook: 'uponSanitizeAttribute', cb: (currentNode: Element, data: DOMPurifySanitizeAttributeHookEvent, config: DOMPurifyConfig) => void): void;
     addHook(hook: DOMPurifyHookName, cb: (currentNode: Element, data: DOMPurifyHookEvent, config: DOMPurifyConfig) => void): void;
diff --git a/types/dompurify/tsconfig.json b/types/dompurify/tsconfig.json
index 44703bdcd5..34d380baf0 100644
--- a/types/dompurify/tsconfig.json
+++ b/types/dompurify/tsconfig.json
@@ -7,7 +7,7 @@
         ],
         "noImplicitAny": true,
         "noImplicitThis": true,
-        "strictNullChecks": false,
+        "strictNullChecks": true,
         "baseUrl": "../",
         "typeRoots": [
             "../"
