diff --git a/src/main/java/io/kamax/mxisd/exception/InvalidParamException.java b/src/main/java/io/kamax/mxisd/exception/InvalidParamException.java
index 571329f..05fca83 100644
--- a/src/main/java/io/kamax/mxisd/exception/InvalidParamException.java
+++ b/src/main/java/io/kamax/mxisd/exception/InvalidParamException.java
@@ -23,5 +23,6 @@ package io.kamax.mxisd.exception;
 public class InvalidParamException extends RuntimeException {
 
     public InvalidParamException() {
+        super("The chosen hash algorithm is invalid or disallowed");
     }
 }
diff --git a/src/main/java/io/kamax/mxisd/exception/InvalidPepperException.java b/src/main/java/io/kamax/mxisd/exception/InvalidPepperException.java
index 59bc1ff..34078b4 100644
--- a/src/main/java/io/kamax/mxisd/exception/InvalidPepperException.java
+++ b/src/main/java/io/kamax/mxisd/exception/InvalidPepperException.java
@@ -23,5 +23,6 @@ package io.kamax.mxisd.exception;
 public class InvalidPepperException extends RuntimeException {
 
     public InvalidPepperException() {
+        super("The provided pepper is invalid or expired");
     }
 }
diff --git a/src/main/java/io/kamax/mxisd/http/undertow/handler/BasicHttpHandler.java b/src/main/java/io/kamax/mxisd/http/undertow/handler/BasicHttpHandler.java
index 46e6c31..59df3b7 100644
--- a/src/main/java/io/kamax/mxisd/http/undertow/handler/BasicHttpHandler.java
+++ b/src/main/java/io/kamax/mxisd/http/undertow/handler/BasicHttpHandler.java
@@ -189,7 +189,7 @@ public abstract class BasicHttpHandler implements HttpHandler {
     }
 
     protected void respond(HttpServerExchange ex, int status, String errCode, String error) {
-        respond(ex, status, buildErrorBody(ex, errCode, error));
+        respond(ex, status, buildErrorBody(ex, errCode, error != null ? error : "An error has occurred"));
     }
 
     protected void handleException(HttpServerExchange exchange, HttpMatrixException ex) {