diff --git a/src/DynamicExpresso.Core/Parsing/Parser.cs b/src/DynamicExpresso.Core/Parsing/Parser.cs
index 1ae3e6fe..ce9a04f4 100644
--- a/src/DynamicExpresso.Core/Parsing/Parser.cs
+++ b/src/DynamicExpresso.Core/Parsing/Parser.cs
@@ -1230,6 +1230,10 @@ private bool TryParseKnownType(string name, out Type type)
 		// we found a known type identifier, check if it has some modifiers
 		private Type ParseTypeModifiers(Type type)
 		{
+			// type modifiers require the base type to be known
+			if (type == null)
+				return null;
+
 			var errorPos = _token.pos;
 			if (_token.id == TokenId.Question)
 			{
diff --git a/test/DynamicExpresso.UnitTest/GithubIssues.cs b/test/DynamicExpresso.UnitTest/GithubIssues.cs
index 0d590542..ab5626a7 100644
--- a/test/DynamicExpresso.UnitTest/GithubIssues.cs
+++ b/test/DynamicExpresso.UnitTest/GithubIssues.cs
@@ -347,6 +347,26 @@ public void GitHub_Issue_169_quatro()
 			Assert.AreEqual("56", result);
 		}
 
+		[Test]
+		public void GitHub_Issue_197()
+		{
+			var interpreterWithLambdas = new Interpreter(InterpreterOptions.DefaultCaseInsensitive | InterpreterOptions.LambdaExpressions);
+			var interpreterWithoutLambdas = new Interpreter(InterpreterOptions.DefaultCaseInsensitive);
+
+			var stringExpression = "booleanValue ? someStringValue : \".\"";
+			var parameters = new List<Parameter>
+			{
+				new Parameter($"someStringValue", typeof(string), $"E33"),
+				new Parameter("booleanValue", typeof(bool), true)
+			};
+
+			var expressionWithoutLambdas = interpreterWithoutLambdas.Parse(stringExpression, typeof(void), parameters.ToArray());
+			Assert.AreEqual("E33", expressionWithoutLambdas.Invoke(parameters.ToArray()));
+
+			var expressionWithLambdas = interpreterWithLambdas.Parse(stringExpression, typeof(void), parameters.ToArray());
+			Assert.AreEqual("E33", expressionWithLambdas.Invoke(parameters.ToArray()));
+		}
+
 		[Test]
 		public void GitHub_Issue_185()
 		{