diff --git a/application/Espo/Core/Formula/Parser.php b/application/Espo/Core/Formula/Parser.php
index fa65a8eb94..13d63f1005 100644
--- a/application/Espo/Core/Formula/Parser.php
+++ b/application/Espo/Core/Formula/Parser.php
@@ -868,7 +868,7 @@ class Parser
                 $offset = -1;
 
                 while (true) {
-                    $index = strrpos($expression, $operator, $offset);
+                    $index = strrpos($modifiedExpression, $operator, $offset);
 
                     if ($index === false) {
                         break;
@@ -889,7 +889,7 @@ class Parser
 
                 if (strlen($operator) === 1) {
                     if ($index < strlen($expression) - 1) {
-                        $possibleRightOperator = trim($operator . $expression[$index + 1]);
+                        $possibleRightOperator = trim($operator . $modifiedExpression[$index + 1]);
                     }
                 }
 
@@ -905,7 +905,7 @@ class Parser
 
                 if (strlen($operator) === 1) {
                     if ($index > 0) {
-                        $possibleLeftOperator = trim($expression[$index - 1] . $operator);
+                        $possibleLeftOperator = trim($modifiedExpression[$index - 1] . $operator);
                     }
                 }
 
diff --git a/tests/unit/Espo/Core/Formula/EvaluatorTest.php b/tests/unit/Espo/Core/Formula/EvaluatorTest.php
index e3ff07f0d0..3ae7abd348 100644
--- a/tests/unit/Espo/Core/Formula/EvaluatorTest.php
+++ b/tests/unit/Espo/Core/Formula/EvaluatorTest.php
@@ -1568,4 +1568,16 @@ class EvaluatorTest extends TestCase
         /** @noinspection PhpUnhandledExceptionInspection */
         $this->evaluator->processSafe($expression);
     }
+
+    public function testStringsWithOperator(): void
+    {
+        $expression = "\$a = '='";
+
+        $vars = (object) [];
+
+        /** @noinspection PhpUnhandledExceptionInspection */
+        $this->evaluator->process($expression, null, $vars);
+
+        $this->assertEquals("=", $vars->a);
+    }
 }