diff --git a/src/lib/Matrix2D.ts b/src/lib/Matrix2D.ts
index 5bd8d3a8..a31df345 100644
--- a/src/lib/Matrix2D.ts
+++ b/src/lib/Matrix2D.ts
@@ -4,7 +4,14 @@
  */
 const DEG_TO_RAD = Math.PI / 180;
 
-export const identity = [1, 0, 0, 1, 0, 0];
+export const identity: [number, number, number, number, number, number] = [
+  1,
+  0,
+  0,
+  1,
+  0,
+  0,
+];
 
 let a = 1;
 let b = 0;
@@ -44,7 +51,7 @@ export function reset() {
  * @method toArray
  * @return {Array} an array with current matrix values.
  **/
-export function toArray() {
+export function toArray(): [number, number, number, number, number, number] {
   if (hasInitialState) {
     return identity;
   }
diff --git a/src/lib/extract/extractTransform.ts b/src/lib/extract/extractTransform.ts
index 94f4a93b..3a2ccfbc 100644
--- a/src/lib/extract/extractTransform.ts
+++ b/src/lib/extract/extractTransform.ts
@@ -33,7 +33,7 @@ function universal2axis(
   axisX: NumberProp | void,
   axisY: NumberProp | void,
   defaultValue?: number,
-) {
+): [number, number] {
   let x;
   let y;
   if (typeof universal === 'number') {
@@ -108,7 +108,7 @@ export function props2transform(props: TransformProps): TransformedProps {
 export function transformToMatrix(
   props: TransformedProps,
   transform: number[] | string | TransformProps | void | undefined,
-) {
+): [number, number, number, number, number, number] {
   reset();
   appendTransformProps(props);
 
diff --git a/src/xml.tsx b/src/xml.tsx
index 1a7c8770..de8f9940 100644
--- a/src/xml.tsx
+++ b/src/xml.tsx
@@ -247,7 +247,7 @@ const validNameCharacters = /[a-zA-Z0-9:_-]/;
 const whitespace = /[\s\t\r\n]/;
 const quotemarks = /['"]/;
 
-export function parse(source: string) {
+export function parse(source: string): AST | null {
   const length = source.length;
   let currentElement: AST | null = null;
   let state = metadata;