diff --git a/java/google/registry/model/registrar/Registrar.java b/java/google/registry/model/registrar/Registrar.java
index e69d3b140..7dc4f3677 100644
--- a/java/google/registry/model/registrar/Registrar.java
+++ b/java/google/registry/model/registrar/Registrar.java
@@ -698,8 +698,8 @@ public class Registrar extends ImmutableObject implements Buildable, Jsonifiable
         ImmutableMap.Builder<CurrencyUnit, BillingAccountEntry> billingAccountMapBuilder =
             new ImmutableMap.Builder<>();
         for (Map.Entry<CurrencyUnit, String> entry : billingAccountMap.entrySet()) {
-          CurrencyUnit key = entry.getKey();
-          billingAccountMapBuilder.put(key, new BillingAccountEntry(key, entry.getValue()));
+          billingAccountMapBuilder.put(
+              entry.getKey(), new BillingAccountEntry(entry.getKey(), entry.getValue()));
         }
         getInstance().billingAccountMap = billingAccountMapBuilder.build();
       }
diff --git a/java/google/registry/tools/CreateOrUpdateRegistrarCommand.java b/java/google/registry/tools/CreateOrUpdateRegistrarCommand.java
index 39123cd60..3c88eca62 100644
--- a/java/google/registry/tools/CreateOrUpdateRegistrarCommand.java
+++ b/java/google/registry/tools/CreateOrUpdateRegistrarCommand.java
@@ -47,6 +47,7 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -182,7 +183,8 @@ abstract class CreateOrUpdateRegistrarCommand extends MutatingCommand {
     description =
         "Registrar Billing Account key-value pairs (formatted as key=value[,key=value...]), "
             + "where key is a currency unit (USD, JPY, etc) and value is the registrar's billing "
-            + "account id for that currency.",
+            + "account id for that currency. During update, only the pairs that need updating need "
+            + "to be provided.",
     converter = CurrencyUnitToStringMap.class,
     validateWith = CurrencyUnitToStringMap.class
   )
@@ -354,7 +356,12 @@ abstract class CreateOrUpdateRegistrarCommand extends MutatingCommand {
         builder.setBillingIdentifier(billingId.orNull());
       }
       if (billingAccountMap != null) {
-        builder.setBillingAccountMap(billingAccountMap);
+        LinkedHashMap<CurrencyUnit, String> newBillingAccountMap = new LinkedHashMap<>();
+        if (oldRegistrar != null && oldRegistrar.getBillingAccountMap() != null) {
+          newBillingAccountMap.putAll(oldRegistrar.getBillingAccountMap());
+        }
+        newBillingAccountMap.putAll(billingAccountMap);
+        builder.setBillingAccountMap(newBillingAccountMap);
       }
       if (billingMethod != null) {
         if (oldRegistrar != null && !billingMethod.equals(oldRegistrar.getBillingMethod())) {
diff --git a/javatests/google/registry/tools/UpdateRegistrarCommandTest.java b/javatests/google/registry/tools/UpdateRegistrarCommandTest.java
index aabf08a9f..6d1b29763 100644
--- a/javatests/google/registry/tools/UpdateRegistrarCommandTest.java
+++ b/javatests/google/registry/tools/UpdateRegistrarCommandTest.java
@@ -26,6 +26,7 @@ import static org.joda.time.DateTimeZone.UTC;
 
 import com.beust.jcommander.ParameterException;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import google.registry.model.billing.RegistrarBillingEntry;
 import google.registry.model.registrar.Registrar;
@@ -225,6 +226,7 @@ public class UpdateRegistrarCommandTest extends CommandTestCase<UpdateRegistrarC
         "NewRegistrar");
   }
 
+  @Test
   public void testSuccess_billingAccountMap_onlyAppliesToRealRegistrar() throws Exception {
     createTlds("foo");
     assertThat(loadByClientId("NewRegistrar").getBillingAccountMap()).isEmpty();
@@ -237,6 +239,20 @@ public class UpdateRegistrarCommandTest extends CommandTestCase<UpdateRegistrarC
         .containsExactly(CurrencyUnit.JPY, "789xyz");
   }
 
+  @Test
+  public void testSuccess_billingAccountMap_partialUpdate() throws Exception {
+    createTlds("foo");
+    persistResource(
+        loadByClientId("NewRegistrar")
+            .asBuilder()
+            .setBillingAccountMap(
+                ImmutableMap.of(CurrencyUnit.USD, "abc123", CurrencyUnit.JPY, "789xyz"))
+            .build());
+    runCommand("--billing_account_map=JPY=123xyz", "--allowed_tlds=foo", "--force", "NewRegistrar");
+    assertThat(loadByClientId("NewRegistrar").getBillingAccountMap())
+        .containsExactly(CurrencyUnit.JPY, "123xyz", CurrencyUnit.USD, "abc123");
+  }
+
   @Test
   public void testSuccess_changeBillingMethodToBraintreeWhenBalanceIsZero() throws Exception {
     createTlds("xn--q9jyb4c");