diff --git a/src/libbson/tests/json/bson_binary_vector/packed_bit.json b/src/libbson/tests/json/bson_binary_vector/packed_bit.json
index a220e7e318e..3015acba660 100644
--- a/src/libbson/tests/json/bson_binary_vector/packed_bit.json
+++ b/src/libbson/tests/json/bson_binary_vector/packed_bit.json
@@ -21,23 +21,32 @@
       "canonical_bson": "1600000005766563746F7200040000000910007F0700"
     },
     {
-      "description": "Empty Vector PACKED_BIT",
+      "description": "PACKED_BIT with padding",
       "valid": true,
-      "vector": [],
+      "vector": [127, 8],
       "dtype_hex": "0x10",
       "dtype_alias": "PACKED_BIT",
-      "padding": 0,
-      "canonical_bson": "1400000005766563746F72000200000009100000"
+      "padding": 3,
+      "canonical_bson": "1600000005766563746F7200040000000910037F0800"
     },
     {
-      "description": "PACKED_BIT with padding",
-      "valid": true,
+      "description": "PACKED_BIT with inconsistent padding",
+      "valid": false,
       "vector": [127, 7],
       "dtype_hex": "0x10",
       "dtype_alias": "PACKED_BIT",
       "padding": 3,
       "canonical_bson": "1600000005766563746F7200040000000910037F0700"
     },
+    {
+      "description": "Empty Vector PACKED_BIT",
+      "valid": true,
+      "vector": [],
+      "dtype_hex": "0x10",
+      "dtype_alias": "PACKED_BIT",
+      "padding": 0,
+      "canonical_bson": "1400000005766563746F72000200000009100000"
+    },
     {
       "description": "Overflow Vector PACKED_BIT",
       "valid": false,
diff --git a/src/libbson/tests/test-bson-vector.c b/src/libbson/tests/test-bson-vector.c
index 81254810b04..c355ada92c7 100644
--- a/src/libbson/tests/test-bson-vector.c
+++ b/src/libbson/tests/test-bson-vector.c
@@ -123,6 +123,20 @@ append_vector_packed_bit_from_packed_array (
          ASSERT (bson_iter_next (&copy_iter));
          uint8_t packed_byte = (uint8_t) bson_iter_as_int64 (&copy_iter);
          ASSERT (bson_vector_packed_bit_view_write_packed (view, &packed_byte, 1, i));
+
+         // Read back the packed byte, interpret any masking as a conversion failure.
+         uint8_t packed_byte_check;
+         ASSERT (bson_vector_packed_bit_view_read_packed (view, &packed_byte_check, 1, i));
+         if (packed_byte != packed_byte_check) {
+            bson_set_error (error,
+                            TEST_ERROR_DOMAIN,
+                            TEST_ERROR_CODE,
+                            "byte at index %zu with value 0x%02X included write to masked bits (reads as 0x%02X)",
+                            i,
+                            packed_byte,
+                            packed_byte_check);
+            return false;
+         }
       }
       return true;
    } else {
@@ -159,17 +173,6 @@ test_bson_vector_json_case (vector_json_test_case_t *test_case)
    bson_error_t vector_from_array_error;
    bool vector_from_array_ok;
 
-   // (Spec test improvement TODO) Patch test cases that have unused bits set to '1' when '0' is required.
-   if (0 == strcmp ("PACKED_BIT with padding", test_case->test_description)) {
-      bson_iter_t iter;
-      ASSERT (bson_iter_init_find (&iter, &expected_bson, test_case->scenario_test_key));
-      uint32_t binary_len;
-      uint8_t *binary;
-      bson_iter_overwrite_binary (&iter, BSON_SUBTYPE_VECTOR, &binary_len, &binary);
-      ASSERT (binary_len > BSON_VECTOR_HEADER_LEN);
-      binary[binary_len - 1] &= (uint8_t) 0xFF << bson_vector_padding_from_header_byte_1 (binary[1]);
-   }
-
    // Try a format conversion from array to the indicated vector format.
    // The spec calls the first header byte "dtype" (combining the element type and element size fields)
    if (0 == strcmp ("0x03", test_case->test_dtype_hex_str)) {
@@ -336,14 +339,6 @@ test_bson_vector_json_case (vector_json_test_case_t *test_case)
                test_error ("test-vector array element %d has unexpected type, should be int.", (int) byte_count);
             }
 
-            // (Spec test improvement TODO) Packed writes can't set unused bits to '1' in libbson, but the spec
-            // tests allow padding bits to take on undefined values. Modify the expected values to keep padding bits
-            // zeroed.
-            if (0 == strcmp ("PACKED_BIT with padding", test_case->test_description) &&
-                byte_count == bson_vector_packed_bit_const_view_length_bytes (actual_view) - 1u) {
-               expected_byte &= ((int64_t) 0xFF << *test_case->test_padding) & 0xFF;
-            }
-
             // Note, the zero initializer is only needed due to a false positive -Wmaybe-uninitialized warning in
             // uncommon configurations where the compiler does not have visibility into memcpy().
             uint8_t actual_byte = 0;