diff --git a/src/core/processing/qgsprocessingparameters.cpp b/src/core/processing/qgsprocessingparameters.cpp
index a68499c300c1..8c2af24f9e6c 100644
--- a/src/core/processing/qgsprocessingparameters.cpp
+++ b/src/core/processing/qgsprocessingparameters.cpp
@@ -1579,6 +1579,10 @@ QStringList QgsProcessingParameters::parameterAsFields( const QgsProcessingParam
       for ( const QVariant &var : constToList )
         resultStringList << var.toString();
     }
+    else if ( val.type() == QVariant::StringList )
+    {
+      resultStringList = val.toStringList();
+    }
     else
       resultStringList.append( val.toString().split( ';' ) );
   }
@@ -1595,6 +1599,10 @@ QStringList QgsProcessingParameters::parameterAsFields( const QgsProcessingParam
         for ( const QVariant &var : constToList )
           resultStringList << var.toString();
       }
+      else if ( definition->defaultValue().type() == QVariant::StringList )
+      {
+        resultStringList = definition->defaultValue().toStringList();
+      }
       else
         resultStringList.append( definition->defaultValue().toString().split( ';' ) );
     }
diff --git a/tests/src/analysis/testqgsprocessing.cpp b/tests/src/analysis/testqgsprocessing.cpp
index be007c1575ff..2b0d6d383d6d 100644
--- a/tests/src/analysis/testqgsprocessing.cpp
+++ b/tests/src/analysis/testqgsprocessing.cpp
@@ -4879,6 +4879,18 @@ void TestQgsProcessing::parameterField()
   fields = QgsProcessingParameters::parameterAsFields( def.get(), params, context );
   QCOMPARE( fields, QStringList() << "def" );
 
+  // optional with string list default
+  def.reset( new QgsProcessingParameterField( "optional", QString(), QStringList() << QStringLiteral( "def" ) << QStringLiteral( "abc" ), QString(), QgsProcessingParameterField::Any, true, true ) );
+  QVERIFY( def->checkValueIsAcceptable( QStringList() << "a" << "b" ) );
+  fields = QgsProcessingParameters::parameterAsFields( def.get(), params, context );
+  QCOMPARE( fields, QStringList() << "def" << "abc" );
+  params.insert( "optional",  QVariantList() << "f" << "h" );
+  fields = QgsProcessingParameters::parameterAsFields( def.get(), params, context );
+  QCOMPARE( fields, QStringList() << "f" << "h" );
+  params.insert( "optional",  QStringList() << "g" << "h" );
+  fields = QgsProcessingParameters::parameterAsFields( def.get(), params, context );
+  QCOMPARE( fields, QStringList() << "g" << "h" );
+
   // optional, no default
   def.reset( new QgsProcessingParameterField( "optional", QString(), QVariant(), QString(), QgsProcessingParameterField::Any, false, true ) );
   params.insert( "optional",  QVariant() );