diff --git a/ext/typeexpr/get_type.go b/ext/typeexpr/get_type.go
index 98a861e9..890cf8ed 100644
--- a/ext/typeexpr/get_type.go
+++ b/ext/typeexpr/get_type.go
@@ -249,7 +249,7 @@ func getType(expr hcl.Expression, constraint, withDefaults bool) (cty.Type, *Def
 			// If a default is set for an optional attribute, verify that it is
 			// convertible to the attribute type.
 			if defaultVal, ok := defaultValues[attrName]; ok {
-				_, err := convert.Convert(defaultVal, aty)
+				convertedDefaultVal, err := convert.Convert(defaultVal, aty)
 				if err != nil {
 					diags = append(diags, &hcl.Diagnostic{
 						Severity: hcl.DiagError,
@@ -258,6 +258,8 @@ func getType(expr hcl.Expression, constraint, withDefaults bool) (cty.Type, *Def
 						Subject:  defaultExpr.Range().Ptr(),
 					})
 					delete(defaultValues, attrName)
+				} else {
+					defaultValues[attrName] = convertedDefaultVal
 				}
 			}
 
diff --git a/ext/typeexpr/get_type_test.go b/ext/typeexpr/get_type_test.go
index 2dca23d2..0249dffb 100644
--- a/ext/typeexpr/get_type_test.go
+++ b/ext/typeexpr/get_type_test.go
@@ -504,7 +504,9 @@ func TestGetTypeDefaults(t *testing.T) {
 					}, []string{"b"}),
 				}, []string{"a"}),
 				DefaultValues: map[string]cty.Value{
-					"a": cty.EmptyObjectVal,
+					"a": cty.ObjectVal(map[string]cty.Value{
+						"b": cty.NullVal(cty.Number),
+					}),
 				},
 				Children: map[string]*Defaults{
 					"a": {