diff --git a/src/zip.cpp b/src/zip.cpp
index 8139673..4020145 100644
--- a/src/zip.cpp
+++ b/src/zip.cpp
@@ -39,6 +39,7 @@ namespace epubgrep::zip
 
 using boost::locale::translate;
 using fmt::format;
+using std::cerr;
 
 std::vector<std::string> list(const fs::path &filepath)
 {
@@ -112,8 +113,19 @@ std::string read_file(const fs::path &filepath, std::string_view entry_path)
 
     close_file(zipfile, filepath);
 
-    throw exception{format(translate("{0:s} not found in {1:s}.").str(),
+    if (entry_path == "META-INF/container.xml")
+    { // File is probably not an EPUB.
+        exception e{format(translate("{0:s} not found in {1:s}.").str(),
                            entry_path, filepath.string())};
+        e.code = 1;
+        throw exception{e};
+    }
+
+    cerr << translate("WARNING: ")
+         << format(translate("{0:s} not found in {1:s}.").str(), entry_path,
+                   filepath.string())
+         << '\n';
+    return {};
 }
 
 struct archive *open_file(const fs::path &filepath)