diff --git a/sklearn2pmml/preprocessing/__init__.py b/sklearn2pmml/preprocessing/__init__.py
index f96532d..d180d9b 100644
--- a/sklearn2pmml/preprocessing/__init__.py
+++ b/sklearn2pmml/preprocessing/__init__.py
@@ -573,6 +573,9 @@ class RegExTransformer(BaseEstimator, TransformerMixin):
 	def __init__(self, pattern, re_flavour):
 		super(RegExTransformer, self).__init__()
 		self.pattern = pattern
+		re_flavours = ["pcre", "pcre2", "re"]
+		if re_flavour not in re_flavours:
+			raise ValueError("Regular Expressions flavour {0} not in {1}".format(re_flavour, re_flavours))
 		self.re_flavour = re_flavour
 
 	def _regex_func(self, regex_engine):
@@ -592,7 +595,7 @@ def transform(self, X):
 class MatchesTransformer(RegExTransformer):
 	"""Match RE pattern."""
 
-	def __init__(self, pattern, re_flavour = None):
+	def __init__(self, pattern, re_flavour = "re"):
 		super(MatchesTransformer, self).__init__(pattern = pattern, re_flavour = re_flavour)
 
 	def _regex_func(self, regex_engine):
@@ -604,7 +607,7 @@ def matches(x):
 class ReplaceTransformer(RegExTransformer):
 	"""Replace all RE pattern matches."""
 
-	def __init__(self, pattern, replacement, re_flavour = None):
+	def __init__(self, pattern, replacement, re_flavour = "re"):
 		super(ReplaceTransformer, self).__init__(pattern = pattern, re_flavour = re_flavour)
 		self.replacement = replacement
 
diff --git a/sklearn2pmml/preprocessing/regex.py b/sklearn2pmml/preprocessing/regex.py
index c2eb6cd..15d14e9 100644
--- a/sklearn2pmml/preprocessing/regex.py
+++ b/sklearn2pmml/preprocessing/regex.py
@@ -59,15 +59,6 @@ def replace(self, replacement, x):
 		return self.pattern_.substitute(replacement, x)
 
 def make_regex_engine(pattern, re_flavour):
-	if re_flavour is None:
-		try:
-			import pcre2
-
-			re_flavour = "pcre2"
-		except ImportError:
-			warnings.warn("Perl Compatible Regular Expressions (PCRE) library is not available, falling back to built-in Regular Expressions (RE) library. Transformation results might not be reproducible between Python and PMML environments when using more complex patterns", Warning)
-			re_flavour = "re"
-
 	if re_flavour == "pcre":
 		return PCREEngine(pattern)
 	elif re_flavour == "pcre2":
@@ -75,5 +66,4 @@ def make_regex_engine(pattern, re_flavour):
 	elif re_flavour == "re":
 		return REEngine(pattern)
 	else:
-		re_flavours = ["pcre", "pcre2", "re"]
-		raise ValueError("Regular Expressions flavour {0} not in {1}".format(re_flavour, re_flavours))
+		raise ValueError(re_flavour)
diff --git a/sklearn2pmml/preprocessing/tests/__init__.py b/sklearn2pmml/preprocessing/tests/__init__.py
index 0987824..648e080 100644
--- a/sklearn2pmml/preprocessing/tests/__init__.py
+++ b/sklearn2pmml/preprocessing/tests/__init__.py
@@ -657,14 +657,14 @@ class MatchesTransformerTest(TransformerTest):
 
 	def test_transform(self):
 		X = Series(["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"])
-		transformer = MatchesTransformer("ar?y", re_flavour = "re")
+		transformer = MatchesTransformer("ar?y")
 		self.assertEqual([True, True, False, False, True, False, False, False, False, False, False, False], self._transform1d(transformer, X).tolist())
 
 class ReplaceTransformerTest(TransformerTest):
 
 	def test_transform(self):
 		X = Series(["A", "B", "BA", "BB", "BAB", "ABBA", "BBBB"])
-		transformer = ReplaceTransformer("B+", "c", re_flavour = "re")
+		transformer = ReplaceTransformer("B+", "c")
 		self.assertEqual(["A", "c", "cA", "c", "cAc", "AcA", "c"], self._transform1d(transformer, X).tolist())
 		vectorizer = CountVectorizer(token_pattern = r"\w+")
 		pipeline = make_pipeline(transformer, vectorizer)