diff --git a/src/crypto/crypto.h b/src/crypto/crypto.h
index 1ed7582..c0b3d18 100644
--- a/src/crypto/crypto.h
+++ b/src/crypto/crypto.h
@@ -32,7 +32,9 @@ namespace Crypto {
   class CryptoException {
   public:
     string text;
-    CryptoException( string s_text ) : text( s_text ) {};
+    bool fatal;
+    CryptoException( string s_text, bool s_fatal = false )
+      : text( s_text ), fatal( s_fatal ) {};
   };
 
   class Base64Key {
diff --git a/src/frontend/mosh-server.cc b/src/frontend/mosh-server.cc
index d7988c5..27e8e3a 100644
--- a/src/frontend/mosh-server.cc
+++ b/src/frontend/mosh-server.cc
@@ -592,7 +592,11 @@ void serve( int host_fd, Terminal::Complete &terminal, ServerConnection &network
       fprintf( stderr, "%s: %s\n", e.function.c_str(), strerror( e.the_errno ) );
       spin();
     } catch ( Crypto::CryptoException e ) {
-      fprintf( stderr, "Crypto exception: %s\n", e.text.c_str() );
+      if ( e.fatal ) {
+        throw;
+      } else {
+        fprintf( stderr, "Crypto exception: %s\n", e.text.c_str() );
+      }
     }
   }
 }
diff --git a/src/frontend/stmclient.cc b/src/frontend/stmclient.cc
index b191914..5a57783 100644
--- a/src/frontend/stmclient.cc
+++ b/src/frontend/stmclient.cc
@@ -398,9 +398,13 @@ void STMClient::main( void )
       req.tv_nsec = 200000000; /* 0.2 sec */
       nanosleep( &req, NULL );
     } catch ( Crypto::CryptoException e ) {
-      wchar_t tmp[ 128 ];
-      swprintf( tmp, 128, L"Crypto exception: %s", e.text.c_str() );
-      overlays.get_notification_engine().set_notification_string( wstring( tmp ) );
+      if ( e.fatal ) {
+        throw;
+      } else {
+        wchar_t tmp[ 128 ];
+        swprintf( tmp, 128, L"Crypto exception: %s", e.text.c_str() );
+        overlays.get_notification_engine().set_notification_string( wstring( tmp ) );
+      }
     }
   }
 }