diff --git a/Tests/VariableAnalysisSniff/VariableAnalysisTest.php b/Tests/VariableAnalysisSniff/VariableAnalysisTest.php
index e9cf2b11..c259a528 100644
--- a/Tests/VariableAnalysisSniff/VariableAnalysisTest.php
+++ b/Tests/VariableAnalysisSniff/VariableAnalysisTest.php
@@ -793,6 +793,25 @@ public function testValidUndefinedVariableNamesIgnoresUndefinedProperties() {
     $this->assertEquals($expectedWarnings, $lines);
   }
 
+  public function testValidUndefinedVariableRegexpIgnoresUndefinedProperties() {
+    $fixtureFile = $this->getFixture('ClassReferenceFixture.php');
+    $phpcsFile = $this->prepareLocalFileForSniffs($fixtureFile);
+    $phpcsFile->ruleset->setSniffProperty(
+      'VariableAnalysis\Sniffs\CodeAnalysis\VariableAnalysisSniff',
+      'validUndefinedVariableRegexp',
+      '/^undefined_/'
+    );
+    $phpcsFile->process();
+    $lines = $this->getWarningLineNumbersFromFile($phpcsFile);
+    $expectedWarnings = [
+      12,
+      13,
+      24,
+      25
+    ];
+    $this->assertEquals($expectedWarnings, $lines);
+  }
+
   public function testUnusedArgumentsBeforeUsedArgumentsAreFoundIfFalse() {
     $fixtureFile = $this->getFixture('UnusedAfterUsedFixture.php');
     $phpcsFile = $this->prepareLocalFileForSniffs($fixtureFile);
diff --git a/VariableAnalysis/Sniffs/CodeAnalysis/VariableAnalysisSniff.php b/VariableAnalysis/Sniffs/CodeAnalysis/VariableAnalysisSniff.php
index 265a72a4..90ad91db 100644
--- a/VariableAnalysis/Sniffs/CodeAnalysis/VariableAnalysisSniff.php
+++ b/VariableAnalysis/Sniffs/CodeAnalysis/VariableAnalysisSniff.php
@@ -90,6 +90,15 @@ class VariableAnalysisSniff implements Sniff {
    */
   public $validUndefinedVariableNames = null;
 
+  /**
+   *  A PHP regexp string for variables that you want to ignore from undefined
+   *  variable warnings. For example, to ignore the variables `$_junk` and
+   *  `$_unused`, this could be set to `'/^_/'`.
+   *
+   *  @var string|null
+   */
+  public $validUndefinedVariableRegexp = null;
+
   /**
    * Allows unused arguments in a function definition if they are
    * followed by an argument which is used.
@@ -264,6 +273,9 @@ protected function getOrCreateVariableInfo($varName, $currScope) {
       if (in_array($varName, $validUndefinedVariableNames)) {
         $scopeInfo->variables[$varName]->ignoreUndefined = true;
       }
+      if (isset($this->validUndefinedVariableRegexp) && preg_match($this->validUndefinedVariableRegexp, $varName) === 1) {
+        $scopeInfo->variables[$varName]->ignoreUndefined = true;
+      }
     }
     return $scopeInfo->variables[$varName];
   }