diff --git a/src/index.js b/src/index.js
index 355fc0a..bc3bd37 100644
--- a/src/index.js
+++ b/src/index.js
@@ -4,6 +4,7 @@ export * from './first-past'
 export * from './min-version'
 export * from './next-version'
 export * from './prerelease'
+export * from './upper-bound'
 export * from './valid-version-or-range'
 export * from './version-compare'
 export * from './x-sort'
diff --git a/src/test/min-version.test.mjs b/src/test/min-version.test.mjs
index bc40826..e993c56 100644
--- a/src/test/min-version.test.mjs
+++ b/src/test/min-version.test.mjs
@@ -14,6 +14,7 @@ describe('minVersion', () => {
     ['1.0.x', '1.0.0'],
     ['1.0.0-alpha.x', '1.0.0-alpha.0'],
     ['1.0.0-beta.x', '1.0.0-beta.0'],
-    ['1.0.0-rc.x', '1.0.0-rc.0']
+    ['1.0.0-rc.x', '1.0.0-rc.0'],
+    ['1.0.0 - 2', '1.0.0']
   ])('%s => %s', (input, expected) => expect(minVersion(input)).toBe(expected))
 })
diff --git a/src/test/next-version.test.js b/src/test/next-version.test.js
index b41880d..37d9fcc 100644
--- a/src/test/next-version.test.js
+++ b/src/test/next-version.test.js
@@ -5,6 +5,7 @@ import * as ver from '../next-version'
 describe('nextVersion', () => {
   describe('handles semver style', () => {
     test.each([
+      // currVer, increment, expected
       ['1.0.0', undefined, '1.0.1'],
       ['1.0.0-alpha.94', undefined, '1.0.0-alpha.95'],
       ['1.0.0-alpha.94', 'prerelease', '1.0.0-alpha.95'],
diff --git a/src/test/upper-bound.test.mjs b/src/test/upper-bound.test.mjs
new file mode 100644
index 0000000..17ff1fe
--- /dev/null
+++ b/src/test/upper-bound.test.mjs
@@ -0,0 +1,14 @@
+/* global describe expect test */
+import { upperBound } from '../upper-bound'
+
+describe('upperBound', () => {
+  test.each([
+    ['*', '*'],
+    ['1.0.0', '1.0.0'],
+    ['2', '<3.0.0-0'],
+    ['1.0.0 - 2', '<3.0.0-0'],
+    ['1.0.x', '<1.1.0-0'],
+    ['1.0.0-alpha.1', '1.0.0-alpha.1'],
+    ['1.0 - 1.2.3', '1.2.3']
+  ])('%s => %s', (input, expected) => expect(upperBound(input)).toBe(expected))
+})
diff --git a/src/test/valid-version-or-range.test.mjs b/src/test/valid-version-or-range.test.mjs
new file mode 100644
index 0000000..bce3fce
--- /dev/null
+++ b/src/test/valid-version-or-range.test.mjs
@@ -0,0 +1,13 @@
+/* global describe expect test */
+import { validVersionOrRange } from '../valid-version-or-range'
+
+describe('validVersionOrRange', () => {
+  test.each([
+    [{ input : '1.0.0' }, true],
+    [{ input : '1.0.0-alpha.0' }, true],
+    [{ input : '1.0.0-alpha.1' }, true],
+    [{ input : '1.0.0 - 2' }, true],
+    [{ input : '1.0.x', onlyXRange : true }, true],
+    [{ input : '1.0.0-alpha.1' }, true]
+  ])('%s => %s', (input, expected) => expect(validVersionOrRange(input)).toBe(expected))
+})
diff --git a/src/upper-bound.mjs b/src/upper-bound.mjs
new file mode 100644
index 0000000..5c71083
--- /dev/null
+++ b/src/upper-bound.mjs
@@ -0,0 +1,22 @@
+import semver from 'semver'
+
+/**
+ * Finds the ceiling of a range. For '*', the ceiling is '*'. For specific versions or any range capped by a specific
+ * version, the ceiling is that version. For any open-ended range, the ceiling is defined by a '<version>-0' range
+ * function where 'verision-0' least range above the given range.
+ * @param {string} range - The range to find the ceiling for.
+ * @returns {string} - Either '*', a specific version, or a '<version>-0'.
+ */
+const upperBound = (range) => {
+  const normalizedRange = semver.validRange(range)
+  if (normalizedRange === null) {
+    return null
+  }
+
+  const ranges = normalizedRange.split(' ')
+  const upperRange = ranges[ranges.length - 1]
+
+  return upperRange.startsWith('<=') ? upperRange.slice(2) : upperRange
+}
+
+export { upperBound }
diff --git a/src/valid-version-or-range.mjs b/src/valid-version-or-range.mjs
index f6f9f8a..b35e6a3 100644
--- a/src/valid-version-or-range.mjs
+++ b/src/valid-version-or-range.mjs
@@ -8,8 +8,8 @@ const validVersionOrRange = ({
   input = throw new Error("'input' is required."),
   onlyXRange = false
 }) =>
-  (dissallowVersions !== true && semver.valid(input))
+  !!((dissallowVersions !== true && semver.valid(input))
     || (onlyXRange !== true && dissallowRanges !== true && semver.validRange(input))
-    || (onlyXRange === true && input.match(xRangeRE))
+    || (onlyXRange === true && input.match(xRangeRE)))
 
 export { validVersionOrRange }