diff --git a/Modules/Registration/RegistrationMethodsv4/include/itkImageRegistrationMethodv4.h b/Modules/Registration/RegistrationMethodsv4/include/itkImageRegistrationMethodv4.h
index e366877c970..68874af9efc 100644
--- a/Modules/Registration/RegistrationMethodsv4/include/itkImageRegistrationMethodv4.h
+++ b/Modules/Registration/RegistrationMethodsv4/include/itkImageRegistrationMethodv4.h
@@ -532,7 +532,7 @@ class ITK_TEMPLATE_EXPORT ImageRegistrationMethodv4 : public ProcessObject
   SetMetricSamplePoints();
 
   SizeValueType m_CurrentLevel;
-  SizeValueType m_NumberOfLevels;
+  SizeValueType m_NumberOfLevels{ 0 };
   SizeValueType m_CurrentIteration;
   RealType      m_CurrentMetricValue;
   RealType      m_CurrentConvergenceValue;
diff --git a/Modules/Registration/RegistrationMethodsv4/include/itkImageRegistrationMethodv4.hxx b/Modules/Registration/RegistrationMethodsv4/include/itkImageRegistrationMethodv4.hxx
index 54c6a21cdc2..78ec3ed29da 100644
--- a/Modules/Registration/RegistrationMethodsv4/include/itkImageRegistrationMethodv4.hxx
+++ b/Modules/Registration/RegistrationMethodsv4/include/itkImageRegistrationMethodv4.hxx
@@ -99,7 +99,7 @@ ImageRegistrationMethodv4<TFixedImage, TMovingImage, TTransform, TVirtualImage,
   this->ProcessObject::SetNthOutput(0, transformDecorator);
   this->m_OutputTransform = transformDecorator->GetModifiable();
 
-  // By default we set up a 3-level image registration.
+  // Default to a 3-level image registration: force the initialization of the ivars that depend on the number of levels.
   this->SetNumberOfLevels(3);
 
   this->m_ShrinkFactorsPerLevel.resize(this->m_NumberOfLevels);