diff --git a/src/index.ts b/src/index.ts
index d908440..0374e5d 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -21,13 +21,13 @@ function useResizeObserver<T extends HTMLElement>(opts?: {
 
 // Type definition when the hook just passes through the user provided ref.
 function useResizeObserver<T extends HTMLElement>(opts?: {
-  ref: RefObject<T>;
+  ref: RefObject<T> | null;
   onResize?: ResizeHandler;
 }): { ref: RefObject<T> } & ObservedSize;
 
 function useResizeObserver<T>(
   opts: {
-    ref?: RefObject<T>;
+    ref?: RefObject<T> | null;
     onResize?: ResizeHandler;
   } = {}
 ): { ref: RefObject<T> } & ObservedSize {
@@ -69,7 +69,7 @@ function useResizeObserver<T>(
   });
 
   useEffect(() => {
-    if (resizeObserverRef.current) {
+    if (!(ref?.current instanceof Element) || resizeObserverRef.current) {
       return;
     }
 
@@ -103,14 +103,10 @@ function useResizeObserver<T>(
         }
       }
     });
-  }, []);
+  });
 
   useEffect(() => {
-    if (
-      typeof ref !== "object" ||
-      ref === null ||
-      !(ref.current instanceof Element)
-    ) {
+    if (!(ref?.current instanceof Element)) {
       return;
     }
 
diff --git a/tests/basic.tsx b/tests/basic.tsx
index fee11ba..e2fd4a4 100644
--- a/tests/basic.tsx
+++ b/tests/basic.tsx
@@ -145,6 +145,36 @@ describe("Vanilla tests", () => {
     handler.assertSize({ width: 100, height: 200 });
   });
 
+  it("should not initialize a ResizeObserver if no ref is passed", async () => {
+    spyOn(window, "ResizeObserver");
+    const Test: FunctionComponent<HandlerResolverComponentProps> = ({
+      resolveHandler,
+    }) => {
+      const { width, height } = useResizeObserver({ ref: null });
+      const currentSizeRef = useRef<{
+        width: number | undefined;
+        height: number | undefined;
+      }>({ width: undefined, height: undefined });
+      currentSizeRef.current.height = height;
+      currentSizeRef.current.width = width;
+
+      useEffect(() => {
+        resolveHandler(createComponentHandler({ currentSizeRef }));
+      }, []);
+
+      return (
+        <div style={{ width: 100, height: 200 }}>
+          {width}x{height}
+        </div>
+      );
+    };
+
+    await render(Test);
+
+    await delay(50);
+    expect(window.ResizeObserver).not.toHaveBeenCalled();
+  });
+
   it("should be able to reuse the same ref to measure different elements", async () => {
     let switchRefs = (): void => {
       throw new Error(`"switchRefs" should've been implemented by now.`);