diff --git a/Orange/widgets/data/owcreateclass.py b/Orange/widgets/data/owcreateclass.py
index d85f6087f1..ffefb55805 100644
--- a/Orange/widgets/data/owcreateclass.py
+++ b/Orange/widgets/data/owcreateclass.py
@@ -250,7 +250,7 @@ class Warning(widget.OWWidget.Warning):
     class Error(widget.OWWidget.Error):
         class_name_duplicated = Msg("Class name duplicated.")
         class_name_empty = Msg("Class name should not be empty.")
-        invalid_regular_expression = Msg("Invalid regular expression.")
+        invalid_regular_expression = Msg("Invalid regular expression: {}")
 
     def __init__(self):
         super().__init__()
@@ -458,15 +458,15 @@ def class_labels(self):
         return [label_edit.text() or f"C{next(class_count)}"
                 for label_edit, _ in self.line_edits]
 
-    def check_patterns(self):
+    def invalid_patterns(self):
         if not self.regular_expressions:
-            return True
-        for pattern in self.active_rules:
+            return None
+        for _, pattern in self.active_rules:
             try:
-                re.compile(pattern[1])
+                re.compile(pattern)
             except re.error:
-                return False
-        return True
+                return pattern
+        return None
 
     def update_counts(self):
         """Recompute and update the counts of matches."""
@@ -575,8 +575,8 @@ def _set_placeholders():
                     lab_edit.setPlaceholderText(label)
 
         _clear_labels()
-        if not self.check_patterns():
-            self.Error.invalid_regular_expression()
+        if (invalid := self.invalid_patterns()) is not None:
+            self.Error.invalid_regular_expression(invalid)
             return
         self.Error.invalid_regular_expression.clear()
 
@@ -594,8 +594,8 @@ def _set_placeholders():
     def apply(self):
         """Output the transformed data."""
         self.Error.clear()
-        if not self.check_patterns():
-            self.Error.invalid_regular_expression()
+        if (invalid := self.invalid_patterns()) is not None:
+            self.Error.invalid_regular_expression(invalid)
             self.Outputs.data.send(None)
             return
 
diff --git a/Orange/widgets/data/tests/test_owcreateclass.py b/Orange/widgets/data/tests/test_owcreateclass.py
index c0796b0f3e..f265011820 100644
--- a/Orange/widgets/data/tests/test_owcreateclass.py
+++ b/Orange/widgets/data/tests/test_owcreateclass.py
@@ -387,10 +387,10 @@ def test_check_patterns(self):
         widget.line_edits[0][1].setText("[a")
 
         widget.regular_expressions = False
-        self.assertTrue(widget.check_patterns())
+        self.assertIsNone(widget.invalid_patterns())
 
         widget.regular_expressions = True
-        self.assertFalse(widget.check_patterns())
+        self.assertEqual(widget.invalid_patterns(), "[a")
 
     def test_check_re_counts(self):
         widget = self.widget
@@ -407,13 +407,14 @@ def test_check_re_counts(self):
         widget.apply()
         self.assertIsNotNone(self.get_output(self.widget.Outputs.data))
 
-        widget.line_edits[0][1].setText("a[.*a")
+        widget.line_edits[1][1].setText("b[")
         self._check_counts([["", ""], ["", ""], ["", ""]])
         self.assertTrue(widget.Error.invalid_regular_expression.is_shown())
+        self.assertIn("b[", str(widget.Error.invalid_regular_expression))
         widget.apply()
         self.assertIsNone(self.get_output(self.widget.Outputs.data))
 
-        widget.line_edits[0][1].setText("a.*a")
+        widget.line_edits[1][1].setText("b")
         self._check_counts([["45", ""], ["30", "+ 4"], ["26", ""]])
         self.assertFalse(widget.Error.invalid_regular_expression.is_shown())
         widget.apply()
diff --git a/i18n/si/msgs.jaml b/i18n/si/msgs.jaml
index d5a895e0f5..301a197c8e 100644
--- a/i18n/si/msgs.jaml
+++ b/i18n/si/msgs.jaml
@@ -4741,7 +4741,7 @@ widgets/data/owcreateclass.py:
         class `Error`:
             Class name duplicated.: Spremenljivka s tem imenom že obstaja.
             Class name should not be empty.: Ime razreda ne more biti prazno.
-            Invalid regular expression.: Napačen regularni izraz.
+            'Invalid regular expression: {}': 'Napačen regularni izraz: {}'
         def `__init__`:
             class_name: false
             New Class Name: Ime novega razreda