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 22c28a98371..f457c863bc3 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
@@ -12131,4 +12131,10 @@ public class AST2CPPTests extends AST2TestBase {
 	public void testDecltypeAutoReturnType_482225() throws Exception {
 		parseAndCheckBindings();
 	}
+	
+	//	constexpr int waldo = (sizeof(double) % 16);
+	public void testSizeofDouble_506170() throws Exception {
+		BindingAssertionHelper helper = getAssertionHelper();
+		helper.assertVariableValue("waldo", 8);
+	}
 }
diff --git a/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2TestBase.java b/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2TestBase.java
index 574fbefbe8f..0e433e57d87 100644
--- a/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2TestBase.java
+++ b/core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/ast2/AST2TestBase.java
@@ -151,6 +151,7 @@ public class AST2TestBase extends BaseTestCase {
 		map.put("__SIZEOF_SHORT__", "2");
 		map.put("__SIZEOF_INT__", "4");
 		map.put("__SIZEOF_LONG__", "8");
+		map.put("__SIZEOF_DOUBLE__", "8");
 		map.put("__SIZEOF_POINTER__", "8");
 		return map;
 	}
@@ -160,6 +161,7 @@ public class AST2TestBase extends BaseTestCase {
 		map.put("__SIZEOF_SHORT__", "2");
 		map.put("__SIZEOF_INT__", "4");
 		map.put("__SIZEOF_LONG__", "8");
+		map.put("__SIZEOF_DOUBLE__", "8");
 		map.put("__SIZEOF_POINTER__", "8");
 		return map;
 	}
diff --git a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/SizeofCalculator.java b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/SizeofCalculator.java
index afcdf72a2e8..5877d020985 100644
--- a/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/SizeofCalculator.java
+++ b/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/dom/parser/SizeofCalculator.java
@@ -238,8 +238,8 @@ public class SizeofCalculator {
 			return type.isComplex() ? sizeof_complex_float : sizeof_float;
 		case eDouble:
 			return type.isComplex() ?
-					(type.isLong() ? sizeof_long_double : sizeof_double) :
-					(type.isLong() ? sizeof_complex_long_double : sizeof_complex_double);
+					(type.isLong() ? sizeof_complex_long_double : sizeof_complex_double) :
+					(type.isLong() ? sizeof_long_double : sizeof_double);
 		case eFloat128:
 			return type.isComplex() ? sizeof_complex_float128 : sizeof_float128;
 		case eDecimal32: