diff --git a/dflib/src/main/java/com/nhl/dflib/GroupBy.java b/dflib/src/main/java/com/nhl/dflib/GroupBy.java
index a053c6c1..278b2ce5 100644
--- a/dflib/src/main/java/com/nhl/dflib/GroupBy.java
+++ b/dflib/src/main/java/com/nhl/dflib/GroupBy.java
@@ -81,6 +81,10 @@ public DataFrame getGroup(Object key) {
      */
     public Series<Integer> rowNumbers() {
 
+        if(groupsIndex.size() == 0) {
+            return IntSeries.forInts();
+        }
+
         DataFrame[] numberedIndex = new DataFrame[groupsIndex.size()];
 
         int i = 0;
diff --git a/dflib/src/test/java/com/nhl/dflib/DataFrame_GroupBy_WindowFuncsTest.java b/dflib/src/test/java/com/nhl/dflib/DataFrame_GroupBy_WindowFuncsTest.java
index bcbf04f3..cdefd6d5 100644
--- a/dflib/src/test/java/com/nhl/dflib/DataFrame_GroupBy_WindowFuncsTest.java
+++ b/dflib/src/test/java/com/nhl/dflib/DataFrame_GroupBy_WindowFuncsTest.java
@@ -5,6 +5,13 @@
 
 public class DataFrame_GroupBy_WindowFuncsTest {
 
+    @Test
+    public void testGroupBy_RowNumbers_Emtpy() {
+        DataFrame df = DataFrame.newFrame("a", "b", "c").empty();
+        Series<Integer> rn = df.group("a").rowNumbers();
+        new SeriesAsserts(rn).expectData();
+    }
+
     @Test
     public void testGroupBy_RowNumbers0() {
         DataFrame df = DataFrame.newFrame("a", "b", "c").foldByRow(