diff --git a/lib/utils.js b/lib/utils.js
index bd330d45..f2ca198c 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -31,11 +31,11 @@ function isMaintenanceRange(range) {
 }
 
 function getUpperBound(range) {
-  return semver.valid(range) ? range : ((semver.validRange(range) || '').match(/<(\d\.\d\.\d)$/) || [])[1];
+  return semver.valid(range) ? range : ((semver.validRange(range) || '').match(/<(\d+\.\d+\.\d+)$/) || [])[1];
 }
 
 function getLowerBound(range) {
-  return ((semver.validRange(range) || '').match(/(\d\.\d\.\d)/) || [])[1];
+  return ((semver.validRange(range) || '').match(/(\d+\.\d+\.\d+)/) || [])[1];
 }
 
 function highest(version1, version2) {
diff --git a/test/utils.test.js b/test/utils.test.js
index 3afa8c71..8d5c6300 100644
--- a/test/utils.test.js
+++ b/test/utils.test.js
@@ -70,18 +70,30 @@ test('isMaintenanceRange', t => {
 
 test('getUpperBound', t => {
   t.is(getUpperBound('1.x.x'), '2.0.0');
+  t.is(getUpperBound('1.X.X'), '2.0.0');
+  t.is(getUpperBound('10.x.x'), '11.0.0');
   t.is(getUpperBound('1.x'), '2.0.0');
+  t.is(getUpperBound('10.x'), '11.0.0');
   t.is(getUpperBound('1.0.x'), '1.1.0');
+  t.is(getUpperBound('10.0.x'), '10.1.0');
+  t.is(getUpperBound('10.10.x'), '10.11.0');
   t.is(getUpperBound('1.0.0'), '1.0.0');
+  t.is(getUpperBound('10.0.0'), '10.0.0');
 
   t.is(getUpperBound('foo'), undefined);
 });
 
 test('getLowerBound', t => {
   t.is(getLowerBound('1.x.x'), '1.0.0');
+  t.is(getLowerBound('1.X.X'), '1.0.0');
+  t.is(getLowerBound('10.x.x'), '10.0.0');
   t.is(getLowerBound('1.x'), '1.0.0');
+  t.is(getLowerBound('10.x'), '10.0.0');
   t.is(getLowerBound('1.0.x'), '1.0.0');
+  t.is(getLowerBound('10.0.x'), '10.0.0');
+  t.is(getLowerBound('1.10.x'), '1.10.0');
   t.is(getLowerBound('1.0.0'), '1.0.0');
+  t.is(getLowerBound('10.0.0'), '10.0.0');
 
   t.is(getLowerBound('foo'), undefined);
 });