diff --git a/functions/diff.js b/functions/diff.js
index 651a3018..ce9004bd 100644
--- a/functions/diff.js
+++ b/functions/diff.js
@@ -10,11 +10,27 @@ const diff = (version1, version2) => {
     const hasPre = v1.prerelease.length || v2.prerelease.length
     const prefix = hasPre ? 'pre' : ''
     const defaultResult = hasPre ? 'prerelease' : ''
-    for (const key in v1) {
-      if (key === 'major' || key === 'minor' || key === 'patch') {
-        if (v1[key] !== v2[key]) {
-          return prefix + key
-        }
+
+    if (v1.major !== v2.major) {
+      return prefix + 'major'
+    }
+    if (v1.minor !== v2.minor) {
+      return prefix + 'minor'
+    }
+
+    if (v1.patch !== v2.patch) {
+      return prefix + 'patch'
+    }
+
+    if (!v1.prerelease.length || !v2.prerelease.length) {
+      if (v1.patch) {
+        return 'patch'
+      }
+      if (v1.minor) {
+        return 'minor'
+      }
+      if (v1.major) {
+        return 'major'
       }
     }
     return defaultResult // may be undefined
diff --git a/test/functions/diff.js b/test/functions/diff.js
index 2369c98f..11663c95 100644
--- a/test/functions/diff.js
+++ b/test/functions/diff.js
@@ -4,19 +4,25 @@ const diff = require('../../functions/diff')
 test('diff versions test', (t) => {
 //  [version1, version2, result]
 //  diff(version1, version2) -> result
-  [['1.2.3', '0.2.3', 'major'],
+  [
+    ['1.2.3', '0.2.3', 'major'],
+    ['0.2.3', '1.2.3', 'major'],
     ['1.4.5', '0.2.3', 'major'],
     ['1.2.3', '2.0.0-pre', 'premajor'],
+    ['2.0.0-pre', '1.2.3', 'premajor'],
     ['1.2.3', '1.3.3', 'minor'],
     ['1.0.1', '1.1.0-pre', 'preminor'],
     ['1.2.3', '1.2.4', 'patch'],
     ['1.2.3', '1.2.4-pre', 'prepatch'],
-    ['0.0.1', '0.0.1-pre', 'prerelease'],
-    ['0.0.1', '0.0.1-pre-2', 'prerelease'],
-    ['1.1.0', '1.1.0-pre', 'prerelease'],
+    ['0.0.1', '0.0.1-pre', 'patch'],
+    ['0.0.1', '0.0.1-pre-2', 'patch'],
+    ['1.1.0', '1.1.0-pre', 'minor'],
     ['1.1.0-pre-1', '1.1.0-pre-2', 'prerelease'],
     ['1.0.0', '1.0.0', null],
-
+    ['0.0.2-1', '0.0.2', 'patch'],
+    ['0.1.0-1', '0.1.0', 'minor'],
+    ['1.0.0-1', '1.0.0', 'major'],
+    ['0.0.0-1', '0.0.0', 'prerelease'],
   ].forEach((v) => {
     const version1 = v[0]
     const version2 = v[1]