diff --git a/resources/page/pagegroup.go b/resources/page/pagegroup.go
index d4ca8ca41..e07efa7ca 100644
--- a/resources/page/pagegroup.go
+++ b/resources/page/pagegroup.go
@@ -316,7 +316,7 @@ func (p Pages) GroupByParamDate(key string, format string, order ...string) (Pag
 		var r Pages
 
 		for _, p := range pages {
-			param := resource.GetParamToLower(p, key)
+			param := resource.GetParam(p, key)
 			var t time.Time
 
 			if param != nil {
diff --git a/resources/page/pagegroup_test.go b/resources/page/pagegroup_test.go
index 218bd841d..ef0d24471 100644
--- a/resources/page/pagegroup_test.go
+++ b/resources/page/pagegroup_test.go
@@ -34,7 +34,8 @@ var pageGroupTestSources = []pageGroupTestObject{
 	{"/section1/testpage2.md", 3, "2012-01-01", "bar"},
 	{"/section1/testpage3.md", 2, "2012-04-06", "foo"},
 	{"/section2/testpage4.md", 1, "2012-03-02", "bar"},
-	{"/section2/testpage5.md", 1, "2012-04-06", "baz"},
+	// date might also be a full datetime:
+	{"/section2/testpage5.md", 1, "2012-04-06T00:00:00Z", "baz"},
 }
 
 func preparePageGroupTestPages(t *testing.T) Pages {