diff --git a/src/frontend/mosh-client.cc b/src/frontend/mosh-client.cc
index 2c1709c..fa5114b 100644
--- a/src/frontend/mosh-client.cc
+++ b/src/frontend/mosh-client.cc
@@ -124,13 +124,13 @@ int main( int argc, char *argv[] )
     }
 
     client.shutdown();
-  } catch ( Network::NetworkException e ) {
+  } catch ( const Network::NetworkException& e ) {
     fprintf( stderr, "Network exception: %s: %s\r\n",
 	     e.function.c_str(), strerror( e.the_errno ) );
-  } catch ( Crypto::CryptoException e ) {
+  } catch ( const Crypto::CryptoException& e ) {
     fprintf( stderr, "Crypto exception: %s\r\n",
 	     e.text.c_str() );
-  } catch ( std::string s ) {
+  } catch ( const std::string& s ) {
     fprintf( stderr, "Error: %s\r\n", s.c_str() );
   }
 
diff --git a/src/frontend/mosh-server.cc b/src/frontend/mosh-server.cc
index 200535e..6e35eb8 100644
--- a/src/frontend/mosh-server.cc
+++ b/src/frontend/mosh-server.cc
@@ -277,11 +277,11 @@ int main( int argc, char *argv[] )
 
   try {
     return run_server( desired_ip, desired_port, command_path, command_argv, colors, verbose, with_motd );
-  } catch ( Network::NetworkException e ) {
+  } catch ( const Network::NetworkException& e ) {
     fprintf( stderr, "Network exception: %s: %s\n",
 	     e.function.c_str(), strerror( e.the_errno ) );
     return 1;
-  } catch ( Crypto::CryptoException e ) {
+  } catch ( const Crypto::CryptoException& e ) {
     fprintf( stderr, "Crypto exception: %s\n",
 	     e.text.c_str() );
     return 1;
@@ -436,10 +436,10 @@ int run_server( const char *desired_ip, const char *desired_port,
 
     try {
       serve( master, terminal, *network );
-    } catch ( Network::NetworkException e ) {
+    } catch ( const Network::NetworkException& e ) {
       fprintf( stderr, "Network exception: %s: %s\n",
 	       e.function.c_str(), strerror( e.the_errno ) );
-    } catch ( Crypto::CryptoException e ) {
+    } catch ( const Crypto::CryptoException& e ) {
       fprintf( stderr, "Crypto exception: %s\n",
 	       e.text.c_str() );
     }
@@ -689,10 +689,10 @@ void serve( int host_fd, Terminal::Complete &terminal, ServerConnection &network
       }
 
       network.tick();
-    } catch ( Network::NetworkException e ) {
+    } catch ( const Network::NetworkException& e ) {
       fprintf( stderr, "%s: %s\n", e.function.c_str(), strerror( e.the_errno ) );
       spin();
-    } catch ( Crypto::CryptoException e ) {
+    } catch ( const Crypto::CryptoException& e ) {
       if ( e.fatal ) {
         throw;
       } else {
diff --git a/src/network/network.cc b/src/network/network.cc
index 7dfe225..095b188 100644
--- a/src/network/network.cc
+++ b/src/network/network.cc
@@ -172,7 +172,7 @@ Connection::Connection( const char *desired_ip, const char *desired_port ) /* se
   if ( desired_ip_addr != INADDR_ANY ) {
     try {
       if ( try_bind( sock, desired_ip_addr, desired_port_no ) ) { return; }
-    } catch ( NetworkException e ) {
+    } catch ( const NetworkException& e ) {
       struct in_addr sin_addr;
       sin_addr.s_addr = desired_ip_addr;
       fprintf( stderr, "Error binding to IP %s: %s: %s\n",
@@ -184,7 +184,7 @@ Connection::Connection( const char *desired_ip, const char *desired_port ) /* se
   /* now try any local interface */
   try {
     if ( try_bind( sock, INADDR_ANY, desired_port_no ) ) { return; }
-  } catch ( NetworkException e ) {
+  } catch ( const NetworkException& e ) {
     fprintf( stderr, "Error binding to any interface: %s: %s\n",
 	     e.function.c_str(), strerror( e.the_errno ) );
     throw; /* this time it's fatal */
diff --git a/src/tests/encrypt-decrypt.cc b/src/tests/encrypt-decrypt.cc
index 6a74e38..c88bdfb 100644
--- a/src/tests/encrypt-decrypt.cc
+++ b/src/tests/encrypt-decrypt.cc
@@ -58,7 +58,7 @@ void test_bad_decrypt( Session &decryption_session ) {
   bool got_exn = false;
   try {
     decryption_session.decrypt( bad_ct );
-  } catch ( CryptoException e ) {
+  } catch ( const CryptoException& e ) {
     got_exn = true;
 
     /* The "bad decrypt" exception needs to be non-fatal, otherwise we are
@@ -128,7 +128,7 @@ int main( int argc, char *argv[] ) {
   for ( size_t i=0; i<NUM_SESSIONS; i++ ) {
     try {
       test_one_session();
-    } catch ( CryptoException e ) {
+    } catch ( const CryptoException& e ) {
       fprintf( stderr, "Crypto exception: %s\r\n",
                e.text.c_str() );
       fatal_assert( false );