diff --git a/src/main/java/edu/harvard/iq/dataverse/api/AbstractApiBean.java b/src/main/java/edu/harvard/iq/dataverse/api/AbstractApiBean.java
index 2ee5730153e..1c8984f47d3 100644
--- a/src/main/java/edu/harvard/iq/dataverse/api/AbstractApiBean.java
+++ b/src/main/java/edu/harvard/iq/dataverse/api/AbstractApiBean.java
@@ -892,6 +892,8 @@ protected <T> T execCommand( Command<T> cmd ) throws WrappedResponse {
             throw new WrappedResponse(ex, badRequest(ex.getMessage(), ex.getFieldErrors()));
         } catch (InvalidCommandArgumentsException ex) {
             throw new WrappedResponse(ex, error(Status.BAD_REQUEST, ex.getMessage()));
+        } catch (ConflictException ex) {
+            throw new WrappedResponse(ex, conflict(ex.getMessage()));
         } catch (CommandException ex) {
             Logger.getLogger(AbstractApiBean.class.getName()).log(Level.SEVERE, "Error while executing command " + cmd, ex);
             throw new WrappedResponse(ex, error(Status.INTERNAL_SERVER_ERROR, ex.getMessage()));
diff --git a/src/main/java/edu/harvard/iq/dataverse/engine/command/exception/ConflictException.java b/src/main/java/edu/harvard/iq/dataverse/engine/command/exception/ConflictException.java
new file mode 100644
index 00000000000..6927bae630d
--- /dev/null
+++ b/src/main/java/edu/harvard/iq/dataverse/engine/command/exception/ConflictException.java
@@ -0,0 +1,14 @@
+package edu.harvard.iq.dataverse.engine.command.exception;
+
+import edu.harvard.iq.dataverse.engine.command.Command;
+
+/**
+ * An exception raised when a command cannot be executed because it clashes with the current state, e.g. when trying to
+ * create a resource that already exists.
+ */
+public class ConflictException extends CommandException {
+
+    public ConflictException(String message, Command aCommand) {
+        super(message, aCommand);
+    }
+}
diff --git a/src/main/java/edu/harvard/iq/dataverse/engine/command/impl/AssignRoleCommand.java b/src/main/java/edu/harvard/iq/dataverse/engine/command/impl/AssignRoleCommand.java
index db3c41f0f03..4b4c42e15d9 100644
--- a/src/main/java/edu/harvard/iq/dataverse/engine/command/impl/AssignRoleCommand.java
+++ b/src/main/java/edu/harvard/iq/dataverse/engine/command/impl/AssignRoleCommand.java
@@ -16,6 +16,7 @@
 import edu.harvard.iq.dataverse.engine.command.CommandContext;
 import edu.harvard.iq.dataverse.engine.command.DataverseRequest;
 import edu.harvard.iq.dataverse.engine.command.exception.CommandException;
+import edu.harvard.iq.dataverse.engine.command.exception.ConflictException;
 import edu.harvard.iq.dataverse.engine.command.exception.IllegalCommandException;
 import edu.harvard.iq.dataverse.util.BundleUtil;
 
@@ -73,7 +74,7 @@ public RoleAssignment execute(CommandContext ctxt) throws CommandException {
         }
     }
     if(isExistingRole(ctxt)){
-        throw new IllegalCommandException(BundleUtil.getStringFromBundle("datasets.api.grant.role.assignee.has.role.error"), this);
+        throw new ConflictException(BundleUtil.getStringFromBundle("datasets.api.grant.role.assignee.has.role.error"), this);
     }
     // TODO make sure the role is defined on the dataverse.
     RoleAssignment roleAssignment = new RoleAssignment(role, grantee, defPoint, privateUrlToken, anonymizedAccess);
diff --git a/src/test/java/edu/harvard/iq/dataverse/api/DataversesIT.java b/src/test/java/edu/harvard/iq/dataverse/api/DataversesIT.java
index dc658c7134b..632ac39eb4e 100644
--- a/src/test/java/edu/harvard/iq/dataverse/api/DataversesIT.java
+++ b/src/test/java/edu/harvard/iq/dataverse/api/DataversesIT.java
@@ -2867,4 +2867,46 @@ public void testDataverseMetadataLanguage() {
         singleLang.then().assertThat().body("data", equalTo(List.of(Map.of("locale", "en", "title", "English"))));
     }
 
+    @Test
+    public void testAssignRoleOnDataverse() {
+        // Create user
+        Response createUser = UtilIT.createRandomUser();
+        createUser.prettyPrint();
+        String username = UtilIT.getUsernameFromResponse(createUser);
+        String apiToken = UtilIT.getApiTokenFromResponse(createUser);
+
+        // Create collection as that user
+        Response createDataverseResponse = UtilIT.createRandomDataverse(apiToken);
+        createDataverseResponse.prettyPrint();
+        String dataverseAlias = UtilIT.getAliasFromResponse(createDataverseResponse);
+
+        // Create second user
+        Response createSecondUserResponse = UtilIT.createRandomUser();
+        String secondUsername = UtilIT.getUsernameFromResponse(createSecondUserResponse);
+        String secondApiToken = UtilIT.getApiTokenFromResponse(createSecondUserResponse);
+
+        // Let the first user assign a role on their collection to the second user
+        Response grantRoleResponse = UtilIT.grantRoleOnDataverse(dataverseAlias, DataverseRole.DS_CONTRIBUTOR, "@" + secondUsername, apiToken);
+        grantRoleResponse.prettyPrint();
+        grantRoleResponse.then().assertThat().statusCode(OK.getStatusCode());
+
+        // Let the first user assign the same role to the same user again -> 409 Conflict
+        Response grantRoleTwiceResponse = UtilIT.grantRoleOnDataverse(dataverseAlias, DataverseRole.DS_CONTRIBUTOR, "@" + secondUsername, apiToken);
+        grantRoleTwiceResponse.prettyPrint();
+        grantRoleTwiceResponse.then().assertThat().statusCode(CONFLICT.getStatusCode());
+
+        // Clean up
+        Response deleteDataverse = UtilIT.deleteDataverse(dataverseAlias, apiToken);
+        deleteDataverse.prettyPrint();
+        deleteDataverse.then().assertThat().statusCode(OK.getStatusCode());
+
+        Response deleteUserResponse = UtilIT.deleteUser(username);
+        deleteUserResponse.prettyPrint();
+        assertEquals(200, deleteUserResponse.getStatusCode());
+
+        Response deleteSecondUserResponse = UtilIT.deleteUser(secondUsername);
+        deleteSecondUserResponse.prettyPrint();
+        assertEquals(200, deleteSecondUserResponse.getStatusCode());
+    }
+
 }