diff --git a/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPTests.java b/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPTests.java
index fe3fce6..bcf3f34 100644
--- a/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPTests.java
+++ b/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2CPPTests.java
@@ -11382,6 +11382,19 @@
 		parseAndCheckBindings(getAboveComment(), CPP, true /* use GNU extensions */);
 	}
 
+	//	enum class TestEnum : char {
+	//	};
+	//
+	//	void bar(__underlying_type(TestEnum) as) {
+	//	}
+	//
+	//	void foo() {
+	//	  bar('a'); // Invalid arguments 'Candidates are: void bar(@120932903)'
+	//	}
+	public void testUnderlyingType_568625() throws Exception {
+		parseAndCheckBindings(getAboveComment(), CPP, true /* use GNU extensions */);
+	}
+
 	//	void ptrFunc(void*);
 	//	void intFunc(int);
 	//	void foo(int* pi, unsigned i) {
@@ -13636,6 +13649,7 @@
 	//		Test<__is_same(Enum, Enum)>::true_val;
 	//		Test<__is_same(Enum, int)>::false_val;
 	//		Test<__is_same(EnumChar, char)>::false_val;
+	//		Test<__is_same(__underlying_type(EnumChar), char)>::true_val;
 	//
 	//		Test<TemplateArgs<int, bool>::Value>::false_val;
 	//		Test<TemplateArgs<int, int>::Value>::true_val;
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPTemplates.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPTemplates.java
index 96e1d2c..a4a8339 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPTemplates.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPTemplates.java
@@ -1717,12 +1717,7 @@
 			if (type instanceof ICPPUnaryTypeTransformation) {
 				ICPPUnaryTypeTransformation typeTransformation = (ICPPUnaryTypeTransformation) type;
 				IType operand = instantiateType(typeTransformation.getOperand(), context);
-				switch (typeTransformation.getOperator()) {
-				case underlying_type:
-					return TypeTraits.underlyingType(operand);
-				default:
-					return null; // shouldn't happen
-				}
+				return SemanticUtil.applyTypeTransformation(typeTransformation.getOperator(), operand);
 			}
 
 			if (type instanceof CPPClosureType) {
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPVisitor.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPVisitor.java
index 11cc476..80858af 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPVisitor.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/CPPVisitor.java
@@ -236,7 +236,6 @@
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPTemplateParameterMap;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPTemplateTypeArgument;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPTypedef;
-import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPUnaryTypeTransformation;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPUnknownTypeScope;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPVariable;
 import org.eclipse.cdt.internal.core.dom.parser.cpp.CPPVariableTemplate;
@@ -2793,7 +2792,12 @@
 			name = ((IASTEnumerationSpecifier) declSpec).getName();
 		} else if (declSpec instanceof ICPPASTTypeTransformationSpecifier) {
 			ICPPASTTypeTransformationSpecifier spec = (ICPPASTTypeTransformationSpecifier) declSpec;
-			return new CPPUnaryTypeTransformation(spec.getOperator(), createType(spec.getOperand()));
+			IType type = SemanticUtil.applyTypeTransformation(spec.getOperator(), createType(spec.getOperand()));
+			if (type != null)
+				return type;
+
+			return ProblemType.UNRESOLVED_NAME;
+
 		} else if (declSpec instanceof ICPPASTSimpleDeclSpecifier) {
 			ICPPASTSimpleDeclSpecifier spec = (ICPPASTSimpleDeclSpecifier) declSpec;
 			// Check for decltype(expr)
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/SemanticUtil.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/SemanticUtil.java
index f84d285..ebf6c6d 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/SemanticUtil.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/cpp/semantics/SemanticUtil.java
@@ -68,6 +68,7 @@
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPReferenceType;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPSpecialization;
 import org.eclipse.cdt.core.dom.ast.cpp.ICPPTemplateArgument;
+import org.eclipse.cdt.core.dom.ast.cpp.ICPPUnaryTypeTransformation;
 import org.eclipse.cdt.core.index.IIndexBinding;
 import org.eclipse.cdt.core.parser.Keywords;
 import org.eclipse.cdt.core.parser.util.ArrayUtil;
@@ -945,4 +946,13 @@
 		}
 		return result;
 	}
+
+	public static IType applyTypeTransformation(ICPPUnaryTypeTransformation.Operator operator, IType type) {
+		switch (operator) {
+		case underlying_type:
+			return TypeTraits.underlyingType(type);
+		default:
+			return null; // shouldn't happen
+		}
+	}
 }