diff --git a/core/src/main/java/io/grpc/CallOptions.java b/core/src/main/java/io/grpc/CallOptions.java
index 1b8efb2ff1..eb7787a27f 100644
--- a/core/src/main/java/io/grpc/CallOptions.java
+++ b/core/src/main/java/io/grpc/CallOptions.java
@@ -326,7 +326,7 @@ public final class CallOptions {
       newOptions.customOptions[customOptions.length] = new Object[] {key, value};
     } else {
       // Replace an existing option
-      newOptions.customOptions[existingIdx][1] = value;
+      newOptions.customOptions[existingIdx] = new Object[] {key, value};
     }
 
     return newOptions;
diff --git a/core/src/test/java/io/grpc/CallOptionsTest.java b/core/src/test/java/io/grpc/CallOptionsTest.java
index 2a54e406ab..4f37e4fff8 100644
--- a/core/src/test/java/io/grpc/CallOptionsTest.java
+++ b/core/src/test/java/io/grpc/CallOptionsTest.java
@@ -196,6 +196,17 @@ public class CallOptionsTest {
     assertThat(opts.getOption(OPTION_2)).isEqualTo("v2");
   }
 
+  @Test
+  public void withOptionDoesNotMutateOriginal() {
+    CallOptions defaultOpt = CallOptions.DEFAULT;
+    CallOptions opt1 = defaultOpt.withOption(OPTION_1, "v1");
+    CallOptions opt2 = opt1.withOption(OPTION_1, "v2");
+
+    assertThat(defaultOpt.getOption(OPTION_1)).isEqualTo("default");
+    assertThat(opt1.getOption(OPTION_1)).isEqualTo("v1");
+    assertThat(opt2.getOption(OPTION_1)).isEqualTo("v2");
+  }
+
   @Test
   public void withStreamTracerFactory() {
     CallOptions opts1 = CallOptions.DEFAULT.withStreamTracerFactory(tracerFactory1);