diff --git a/src/java_bytecode/jar_file.cpp b/src/java_bytecode/jar_file.cpp
index 28a099ec934..4bab160e83d 100644
--- a/src/java_bytecode/jar_file.cpp
+++ b/src/java_bytecode/jar_file.cpp
@@ -62,17 +62,19 @@ jar_filet &jar_filet::operator=(jar_filet &&other)
   return *this;
 }
 
-std::string jar_filet::get_entry(const std::string &name)
+optionalt<std::string> jar_filet::get_entry(const std::string &name)
 {
   const auto entry=m_name_to_index.find(name);
-  INVARIANT(entry!=m_name_to_index.end(), "File doesn't exist");
+  if(entry==m_name_to_index.end())
+    return {};
+
   try
   {
     return m_zip_archive.extract(entry->second);
   }
   catch(const std::runtime_error &)
   {
-    return "";
+    return {};
   }
 }
 
@@ -96,21 +98,25 @@ static std::string trim(
 
 std::unordered_map<std::string, std::string> jar_filet::get_manifest()
 {
+  const auto entry=get_entry("META-INF/MANIFEST.MF");
+
+  if(!entry.has_value())
+    return {};
+
   std::unordered_map<std::string, std::string> out;
-  const auto entry=m_name_to_index.find("META-INF/MANIFEST.MF");
-  if(entry!=m_name_to_index.end())
+  std::istringstream in(*entry);
+  std::string line;
+  while(std::getline(in, line))
   {
-    std::istringstream in(this->get_entry(entry->first));
-    std::string line;
-    while(std::getline(in, line))
+    const auto key_end=std::find(line.cbegin(), line.cend(), ':');
+    if(key_end!=line.cend())
     {
-      const auto key_end=std::find(line.cbegin(), line.cend(), ':');
-      if(key_end!=line.cend())
-        out.emplace(
-          trim(line.cbegin(), key_end),
-          trim(std::next(key_end), line.cend()));
+      out.emplace(
+        trim(line.cbegin(), key_end),
+        trim(std::next(key_end), line.cend()));
     }
   }
+
   return out;
 }
 
diff --git a/src/java_bytecode/jar_file.h b/src/java_bytecode/jar_file.h
index 61a89a1884c..4cf81d6f4bb 100644
--- a/src/java_bytecode/jar_file.h
+++ b/src/java_bytecode/jar_file.h
@@ -13,6 +13,9 @@ Author: Diffblue Ltd
 #include <memory>
 #include <string>
 #include <vector>
+
+#include <util/optional.h>
+
 #include "mz_zip_archive.h"
 
 class java_class_loader_limitt;
@@ -41,19 +44,23 @@ class jar_filet final
   ~jar_filet()=default;
 
   /// Get contents of a file in the jar archive.
-  /// Terminates the program if file doesn't exist
+  /// Returns nullopt if file doesn't exist.
   /// \param filename Name of the file in the archive
-  std::string get_entry(const std::string &filename);
+  optionalt<std::string> get_entry(const std::string &filename);
+
   /// Get contents of the Manifest file in the jar archive
   std::unordered_map<std::string, std::string> get_manifest();
+
   /// Get list of filenames in the archive
   std::vector<std::string> filenames() const;
+
 private:
   /// Loads the fileindex (m_name_to_index) with a map of loaded files to
   /// indices.
   void initialize_file_index(java_class_loader_limitt &limit);
 
   mz_zip_archivet m_zip_archive;
+
   /// Map of filename to the file index in the zip archive.
   std::unordered_map<std::string, size_t> m_name_to_index;
 };
diff --git a/src/java_bytecode/java_class_loader.cpp b/src/java_bytecode/java_class_loader.cpp
index 6954e963af1..ca9c14f8062 100644
--- a/src/java_bytecode/java_class_loader.cpp
+++ b/src/java_bytecode/java_class_loader.cpp
@@ -91,11 +91,14 @@ optionalt<java_bytecode_parse_treet> java_class_loadert::get_class_from_jar(
   debug()
     << "Getting class `" << class_name << "' from JAR " << jar_file << eom;
 
-  std::string data =
+  auto data =
     jar_pool(class_loader_limit, jar_file).get_entry(jar_index_it->second);
 
+  if(!data.has_value())
+    return {};
+
   java_bytecode_parse_treet parse_tree;
-  std::istringstream istream(data);
+  std::istringstream istream(*data);
   if(java_bytecode_parse(istream, parse_tree, get_message_handler()))
     return {};
   return parse_tree;