diff --git a/main/gradebook/lib/be/category.class.php b/main/gradebook/lib/be/category.class.php
index 0926eb4038..5dcf87e7f6 100644
--- a/main/gradebook/lib/be/category.class.php
+++ b/main/gradebook/lib/be/category.class.php
@@ -996,7 +996,7 @@ class Category implements GradebookItem
 		$evals = array();
 
 		// 1 student
- 		if (isset($stud_id)) {
+ 		if (isset($stud_id) and !empty($stud_id)) {
 			// special case: this is the root
 			if ($this->id == 0) {
 				$evals = Evaluation::get_evaluations_with_result_for_student(0,$stud_id);
@@ -1102,4 +1102,4 @@ class Category implements GradebookItem
 		}
 		return $foundcats;
     }
-}
\ No newline at end of file
+}
diff --git a/main/gradebook/lib/be/evaluation.class.php b/main/gradebook/lib/be/evaluation.class.php
index 02561d7315..21fee328e1 100644
--- a/main/gradebook/lib/be/evaluation.class.php
+++ b/main/gradebook/lib/be/evaluation.class.php
@@ -156,7 +156,7 @@ class Evaluation implements GradebookItem
 			$sql .= ' user_id = '.$user_id;
 			$paramcount ++;
 		}
-		if (isset ($course_code)) {
+		if (isset ($course_code) && $course_code <> '-1') {
 			if ($paramcount != 0) $sql .= ' AND';
 			else $sql .= ' WHERE';
 			$sql .= " course_code = '".$course_code."'";