diff --git a/src/util/irep_serialization.cpp b/src/util/irep_serialization.cpp
index 92f975ef949..5d47191efad 100644
--- a/src/util/irep_serialization.cpp
+++ b/src/util/irep_serialization.cpp
@@ -16,6 +16,7 @@ Date: May 2007
 #include <sstream>
 #include <iostream>
 
+#include "exception_utils.h"
 #include "string_hash.h"
 
 void irep_serializationt::write_irep(
@@ -95,8 +96,7 @@ void irep_serializationt::read_irep(
 
   if(in.get()!=0)
   {
-    std::cerr << "irep not terminated\n";
-    throw 0;
+    throw deserialization_exceptiont("irep not terminated");
   }
 }
 
@@ -150,7 +150,7 @@ std::size_t irep_serializationt::insert_on_read(
       std::pair<bool, irept>(false, get_nil_irep()));
 
   if(ireps_container.ireps_on_read[id].first)
-    throw "irep id read twice.";
+    throw deserialization_exceptiont("irep id read twice.");
   else
   {
     ireps_container.ireps_on_read[id]=
diff --git a/src/util/json_irep.cpp b/src/util/json_irep.cpp
index a3fcac16592..375e06eb82a 100644
--- a/src/util/json_irep.cpp
+++ b/src/util/json_irep.cpp
@@ -11,6 +11,7 @@ Author: Thomas Kiley, thomas.kiley@diffblue.com
 
 #include "json_irep.h"
 
+#include "exception_utils.h"
 #include "irep.h"
 #include "json.h"
 
@@ -103,8 +104,11 @@ irept json_irept::convert_from_json(const jsont &in) const
     have_keys.push_back(keyval.first);
   std::sort(have_keys.begin(), have_keys.end());
   if(have_keys!=std::vector<std::string>{"comment", "id", "namedSub", "sub"})
-    throw "irep JSON representation is missing one of needed keys: "
-      "'id', 'sub', 'namedSub', 'comment'";
+  {
+    throw deserialization_exceptiont(
+      "irep JSON representation is missing one of needed keys: "
+      "'id', 'sub', 'namedSub', 'comment'");
+  }
 
   irept out(in["id"].value);