diff --git a/imap_processing/mag/l1a/mag_l1a_data.py b/imap_processing/mag/l1a/mag_l1a_data.py
index d6b593b48..33a2fafb0 100644
--- a/imap_processing/mag/l1a/mag_l1a_data.py
+++ b/imap_processing/mag/l1a/mag_l1a_data.py
@@ -708,15 +708,15 @@ def process_compressed_vectors(  # noqa: PLR0912, PLR0915
                 secondary_vectors[vector_index] = decoded_vector
                 vector_index += 1
 
-        # TODO: should the range vectors include the first vector?
         if has_range_data_section:
             primary_vectors = MagL1a.process_range_data_section(
-                bit_array[end_vector : end_vector + primary_count * 2], primary_vectors
+                bit_array[end_vector : end_vector + (primary_count - 1) * 2],
+                primary_vectors,
             )
             secondary_vectors = MagL1a.process_range_data_section(
                 bit_array[
-                    end_vector + primary_count * 2 : end_vector
-                    + (primary_count + secondary_count) * 2
+                    end_vector + (primary_count - 1) * 2 : end_vector
+                    + (primary_count + secondary_count - 2) * 2
                 ],
                 secondary_vectors,
             )
@@ -748,17 +748,17 @@ def process_range_data_section(
             Updated array of vectors, identical to vectors with the range values
             updated from range_data.
         """
-        if len(range_data) != len(vectors) * 2:
+        if len(range_data) != (len(vectors) - 1) * 2:
             raise ValueError(
-                "Incorrect length for range_data, there should be two bits per vector."
+                "Incorrect length for range_data, there should be two bits per vector, "
+                "excluding the first."
             )
 
         updated_vectors: np.ndarray = np.copy(vectors)
         range_str = "".join([str(i) for i in range_data])
-        for i in range(len(vectors)):
+        for i in range(len(vectors) - 1):
             range_int = int(range_str[i * 2 : i * 2 + 2], 2)
-            updated_vectors[i][3] = range_int
-
+            updated_vectors[i + 1][3] = range_int
         return updated_vectors
 
     @staticmethod
diff --git a/imap_processing/tests/mag/test_mag_l1a.py b/imap_processing/tests/mag/test_mag_l1a.py
index fcb54079e..42e8288f0 100644
--- a/imap_processing/tests/mag/test_mag_l1a.py
+++ b/imap_processing/tests/mag/test_mag_l1a.py
@@ -360,12 +360,13 @@ def test_compressed_vector_data(expected_vectors):
     assert np.array_equal(secondary, secondary_expected)
 
     # range data has 2 bits per vector, primary and then secondary in sequence.
-    range_primary = "00000000000000000101101011111111"
+    # It excludes the first vector, making the length (primary_count - 1) * 2
+    range_primary = "000000000000000101101011111111"
 
-    expected_range_primary = [0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 3, 3]
+    expected_range_primary = [3, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 3, 3]
 
-    range_secondary = "01000000000000000101101011111101"
-    expected_range_secondary = [1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 3, 1]
+    range_secondary = "000000000000000101101011111101"
+    expected_range_secondary = [3, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 3, 1]
     # 16 bit width with range section
     headers = "01000010"
     # TODO: if there is a number of vectors that is not a multiple of 8,