diff --git a/grib/src/test/data/index/grib-template-3-33.grib.gbx9 b/grib/src/test/data/index/grib-template-3-33.grib.gbx9
new file mode 100644
index 0000000000..03d4a1e983
Binary files /dev/null and b/grib/src/test/data/index/grib-template-3-33.grib.gbx9 differ
diff --git a/grib/src/test/java/ucar/nc2/grib/grib2/TestGdt33.java b/grib/src/test/java/ucar/nc2/grib/grib2/TestGdt33.java
new file mode 100644
index 0000000000..b8cc25211a
--- /dev/null
+++ b/grib/src/test/java/ucar/nc2/grib/grib2/TestGdt33.java
@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2026 University Corporation for Atmospheric Research/Unidata
+ * See LICENSE for license information.
+ */
+
+package ucar.nc2.grib.grib2;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class TestGdt33 {
+
+  private Grib2Record record;
+
+  @Before
+  public void openTestFile() {
+    String testfile = "../grib/src/test/data/index/grib-template-3-33.grib.gbx9";
+
+    Grib2Index gi = new Grib2Index();
+    boolean success = gi.readIndex(testfile, -1);
+    assertThat(success).isTrue();
+    assertThat(gi.getRecords()).hasSize(1);
+    assertThat(gi.getGds()).hasSize(1);
+    record = gi.getRecords().get(0);
+  }
+
+  @Test
+  public void testGdsTemplate() {
+    Grib2Gds gds = record.getGDS();
+    assertThat(gds.template).isEqualTo(33);
+
+    // check that the grid dimensions are parsed out as expected
+    assertThat(gds.getNx()).isEqualTo(1909);
+    assertThat(gds.getNy()).isEqualTo(1609);
+  }
+
+  @Test
+  public void testReferenceDateSanity() {
+    assertEquals("2026-08-01T00:00:00Z", record.getReferenceDate().toString());
+  }
+
+}