diff --git a/src/TodoByVersionRule.php b/src/TodoByVersionRule.php
index 73f972e..6411cc5 100644
--- a/src/TodoByVersionRule.php
+++ b/src/TodoByVersionRule.php
@@ -9,6 +9,7 @@
 use PHPStan\Rules\RuleErrorBuilder;
 use staabm\PHPStanTodoBy\utils\CommentMatcher;
 use staabm\PHPStanTodoBy\utils\ExpiredCommentErrorBuilder;
+use staabm\PHPStanTodoBy\utils\InvalidTagException;
 use staabm\PHPStanTodoBy\utils\LatestTagNotFoundException;
 use staabm\PHPStanTodoBy\utils\ReferenceVersionFinder;
 use UnexpectedValueException;
@@ -82,6 +83,12 @@ public function processNode(Node $node, Scope $scope): array
                         ->identifier(ExpiredCommentErrorBuilder::ERROR_IDENTIFIER_PREFIX.self::ERROR_IDENTIFIER)
                         ->build(),
                 ];
+            } catch (InvalidTagException $e) {
+                return [
+                    RuleErrorBuilder::message($e->getMessage())
+                        ->identifier(ExpiredCommentErrorBuilder::ERROR_IDENTIFIER_PREFIX.self::ERROR_IDENTIFIER)
+                        ->build(),
+                ];
             }
             $provided = $versionParser->parseConstraints(
                 $referenceVersion
@@ -94,7 +101,7 @@ public function processNode(Node $node, Scope $scope): array
 
                 // assume a min version constraint, when the comment does not specify a comparator
                 if (null === $this->getVersionComparator($version)) {
-                    $version = '>='. $version;
+                    $version = '>=' . $version;
                 }
 
                 try {
@@ -118,7 +125,7 @@ public function processNode(Node $node, Scope $scope): array
 
                 // If there is further text, append it.
                 if ('' !== $todoText) {
-                    $errorMessage = "Version requirement {$version} satisfied: ". rtrim($todoText, '.') .'.';
+                    $errorMessage = "Version requirement {$version} satisfied: " . rtrim($todoText, '.') . '.';
                 } else {
                     $errorMessage = "Version requirement {$version} satisfied.";
                 }
@@ -128,7 +135,7 @@ public function processNode(Node $node, Scope $scope): array
                     $comment->getStartLine(),
                     $errorMessage,
                     self::ERROR_IDENTIFIER,
-                    "Calculated reference version is '". $referenceVersion ."'.\n\n   See also:\n https://github.com/staabm/phpstan-todo-by#reference-version",
+                    "Calculated reference version is '" . $referenceVersion . "'.\n\n   See also:\n https://github.com/staabm/phpstan-todo-by#reference-version",
                     $match[0][1]
                 );
             }
diff --git a/src/utils/InvalidTagException.php b/src/utils/InvalidTagException.php
new file mode 100644
index 0000000..6d5a50c
--- /dev/null
+++ b/src/utils/InvalidTagException.php
@@ -0,0 +1,9 @@
+<?php
+
+namespace staabm\PHPStanTodoBy\utils;
+
+use RuntimeException;
+
+final class InvalidTagException extends RuntimeException
+{
+}
diff --git a/src/utils/ReferenceVersionFinder.php b/src/utils/ReferenceVersionFinder.php
index 0cc7cb2..ae3bff4 100644
--- a/src/utils/ReferenceVersionFinder.php
+++ b/src/utils/ReferenceVersionFinder.php
@@ -37,8 +37,10 @@ public function find(?string $workingDirectory): string
     }
 
     // adopted from https://github.com/WyriHaximus/github-action-next-semvers/blob/master/src/Next.php
-    private function nextVersion(string $versionString): string
+    private function nextVersion(string $versionString, ?string $originalVersionString = null): string
     {
+        $originalVersionString ??= $versionString;
+
         try {
             $version = Version::fromString($versionString);
         } catch (InvalidVersionString $invalidVersionException) {
@@ -54,7 +56,11 @@ private function nextVersion(string $versionString): string
                 $versionString .= '.0';
             }
 
-            return self::nextVersion($versionString);
+            try {
+                return $this->nextVersion($versionString, $originalVersionString);
+            } catch (InvalidVersionString $invalidVersionException) {
+                throw new InvalidTagException("Could not parse version from tag '{$originalVersionString}'", 0, $invalidVersionException);
+            }
         }
 
         $wasPreRelease = false;
diff --git a/tests/TodoByVersionRuleNonSemverTagTest.php b/tests/TodoByVersionRuleNonSemverTagTest.php
new file mode 100644
index 0000000..c50bd0f
--- /dev/null
+++ b/tests/TodoByVersionRuleNonSemverTagTest.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace staabm\PHPStanTodoBy\Tests;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+use staabm\PHPStanTodoBy\TodoByVersionRule;
+use staabm\PHPStanTodoBy\utils\ExpiredCommentErrorBuilder;
+use staabm\PHPStanTodoBy\utils\ReferenceVersionFinder;
+
+/**
+ * @extends RuleTestCase<TodoByVersionRule>
+ * @internal
+ */
+final class TodoByVersionRuleNonSemverTagTest extends RuleTestCase
+{
+    private string $referenceVersion;
+
+    protected function getRule(): Rule
+    {
+        return new TodoByVersionRule(
+            true,
+            new ReferenceVersionFinder($this->referenceVersion, new StaticTagFetcher('testing')),
+            new ExpiredCommentErrorBuilder(true)
+        );
+    }
+
+    public function testInvalidTagIsParsed(): void
+    {
+        $this->referenceVersion = 'nextMajor';
+
+        $this->analyse([__DIR__ . '/data/tagNotFound.php'], [
+            [
+                "Could not parse version from tag 'testing'",
+                5,
+            ],
+        ]);
+    }
+}