diff --git a/src/number/sum.ts b/src/number/sum.ts
index 556f90f2..7dc539d1 100644
--- a/src/number/sum.ts
+++ b/src/number/sum.ts
@@ -1,6 +1,8 @@
 /**
- * Sum all numbers in an array. Optionally provide a function to
- * convert objects in the array to number values.
+ * Add up numbers related to an array in 1 of 2 ways:
+ * 1. Sum all numbers in an array of numbers
+ * 2. Sum all numbers returned by a callback function that maps
+ *    each item in an array to a number.
  *
  * @see https://radashi-org.github.io/reference/array/sum
  * @example
@@ -14,14 +16,14 @@
  *   {value: 3}
  * ], (item) => item.value)
  * // => 6
+ *
+ * sum([true, false, true], (item) => item ? 1 : 0)
+ * // => 2
  * ```
  */
-export function sum<T extends number>(array: readonly T[]): number
-export function sum<T extends object>(
-  array: readonly T[],
-  fn: (item: T) => number,
-): number
-export function sum<T extends object | number>(
+export function sum(array: readonly number[]): number
+export function sum<T>(array: readonly T[], fn: (item: T) => number): number
+export function sum<T>(
   array: readonly any[],
   fn?: (item: T) => number,
 ): number {
diff --git a/tests/number/sum.test.ts b/tests/number/sum.test.ts
index 73d9b892..12dbfaa4 100644
--- a/tests/number/sum.test.ts
+++ b/tests/number/sum.test.ts
@@ -17,4 +17,19 @@ describe('sum', () => {
     const result = _.sum(cast(null))
     expect(result).toBe(0)
   })
+  test('gracefully handles boolean input list', () => {
+    const list = [true, false, true, false, true]
+    const result = _.sum(list, x => (x ? 1 : 0))
+    expect(result).toBe(3)
+  })
+
+  test('gracefully handles matrix input', () => {
+    const list = [
+      [1, 2, 3],
+      [4, 5, 6],
+      [7, 8, 9],
+    ]
+    const result = _.sum(list, x => _.sum(x))
+    expect(result).toBe(45)
+  })
 })