diff --git a/src/integrationTest/java/com/marketdata/sdk/MarketsIntegrationTest.java b/src/integrationTest/java/com/marketdata/sdk/MarketsIntegrationTest.java
index 764d484..a441102 100644
--- a/src/integrationTest/java/com/marketdata/sdk/MarketsIntegrationTest.java
+++ b/src/integrationTest/java/com/marketdata/sdk/MarketsIntegrationTest.java
@@ -90,4 +90,22 @@ void statusCountbackWindowDecodes() {
       }
     }
   }
+
+  @Test
+  void statusCountbackReturnsExactlyNDaysEndingAtTo() {
+    // A bare request (no window params) returns a single day — today. countback=5 paired with
+    // `to` must widen that to exactly 5 calendar days ending at `to`, proving the parameter
+    // reached the wire rather than being ignored.
+    LocalDate to = LocalDate.now();
+
+    MarketStatusResponse unfiltered = client.markets().status(MarketStatusRequest.of());
+    MarketStatusResponse countback =
+        client.markets().status(MarketStatusRequest.builder().to(to).countback(5).build());
+
+    assertThat(countback.statusCode()).isIn(200, 203);
+    assertThat(countback.values()).as("countback=5 returns exactly 5 days ending at `to`").hasSize(5);
+    assertThat(countback.values().size())
+        .as("countback widens the result past the unfiltered single-day default")
+        .isGreaterThan(unfiltered.values().size());
+  }
 }
diff --git a/src/test/java/com/marketdata/sdk/MarketsResourceTest.java b/src/test/java/com/marketdata/sdk/MarketsResourceTest.java
index b0c59e6..ff23de9 100644
--- a/src/test/java/com/marketdata/sdk/MarketsResourceTest.java
+++ b/src/test/java/com/marketdata/sdk/MarketsResourceTest.java
@@ -335,6 +335,18 @@ void statusRequestRejectsDateWithRange() {
         .hasMessageContaining("mutually exclusive");
   }
 
+  @Test
+  void statusRequestRejectsCountbackWithDate() {
+    assertThatThrownBy(
+            () ->
+                MarketStatusRequest.builder()
+                    .date(LocalDate.of(2025, Month.JANUARY, 1))
+                    .countback(5)
+                    .build())
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessageContaining("mutually exclusive");
+  }
+
   @Test
   void statusRequestRejectsCountbackWithFrom() {
     assertThatThrownBy(