diff --git a/code/client/cl_input.c b/code/client/cl_input.c
index 72056a28..f0147682 100644
--- a/code/client/cl_input.c
+++ b/code/client/cl_input.c
@@ -863,7 +863,7 @@ void CL_WritePacket( void ) {
 		// also use the message acknowledge
 		key ^= clc.serverMessageSequence;
 		// also use the last acknowledged server command in the key
-		key ^= Com_HashKey(clc.serverCommands[ clc.serverCommandSequence & (MAX_RELIABLE_COMMANDS-1) ], 32);
+		key ^= MSG_HashKey(clc.serverCommands[ clc.serverCommandSequence & (MAX_RELIABLE_COMMANDS-1) ], 32);
 
 		// write all the commands, including the predicted command
 		for ( i = 0 ; i < count ; i++ ) {
diff --git a/code/qcommon/common.c b/code/qcommon/common.c
index 2f4e8438..b8bef851 100644
--- a/code/qcommon/common.c
+++ b/code/qcommon/common.c
@@ -672,22 +672,6 @@ int Com_FilterPath(char *filter, char *name, int casesensitive)
 	return Com_Filter(new_filter, new_name, casesensitive);
 }
 
-/*
-============
-Com_HashKey
-============
-*/
-int Com_HashKey(char *string, int maxlen) {
-	int register hash, i;
-
-	hash = 0;
-	for (i = 0; i < maxlen && string[i] != '\0'; i++) {
-		hash += string[i] * (119 + i);
-	}
-	hash = (hash ^ (hash >> 10) ^ (hash >> 20));
-	return hash;
-}
-
 /*
 ================
 Com_RealTime
diff --git a/code/qcommon/msg.c b/code/qcommon/msg.c
index b883c83b..04fb424a 100644
--- a/code/qcommon/msg.c
+++ b/code/qcommon/msg.c
@@ -311,9 +311,9 @@ void MSG_WriteString( msg_t *sb, const char *s ) {
 		}
 		Q_strncpyz( string, s, sizeof( string ) );
 
-		// get rid of 0xff chars, because old clients don't like them
+		// get rid of 0x80+ and '%' chars, because old clients don't like them
 		for ( i = 0 ; i < l ; i++ ) {
-			if ( ((byte *)string)[i] > 127 ) {
+			if ( ((byte *)string)[i] > 127 || string[i] == '%' ) {
 				string[i] = '.';
 			}
 		}
@@ -337,9 +337,9 @@ void MSG_WriteBigString( msg_t *sb, const char *s ) {
 		}
 		Q_strncpyz( string, s, sizeof( string ) );
 
-		// get rid of 0xff chars, because old clients don't like them
+		// get rid of 0x80+ and '%' chars, because old clients don't like them
 		for ( i = 0 ; i < l ; i++ ) {
-			if ( ((byte *)string)[i] > 127 ) {
+			if ( ((byte *)string)[i] > 127 || string[i] == '%' ) {
 				string[i] = '.';
 			}
 		}
@@ -525,6 +525,21 @@ void MSG_ReadData( msg_t *msg, void *data, int len ) {
 	}
 }
 
+// a string hasher which gives the same hash value even if the
+// string is later modified via the legacy MSG read/write code
+int MSG_HashKey(const char *string, int maxlen) {
+	int hash, i;
+
+	hash = 0;
+	for (i = 0; i < maxlen && string[i] != '\0'; i++) {
+		if (string[i] & 0x80 || string[i] == '%')
+			hash += '.' * (119 + i);
+		else
+			hash += string[i] * (119 + i);
+	}
+	hash = (hash ^ (hash >> 10) ^ (hash >> 20));
+	return hash;
+}
 
 /*
 =============================================================================
diff --git a/code/qcommon/qcommon.h b/code/qcommon/qcommon.h
index a2d81060..d1cc2fde 100644
--- a/code/qcommon/qcommon.h
+++ b/code/qcommon/qcommon.h
@@ -76,6 +76,7 @@ void MSG_WriteFloat (msg_t *sb, float f);
 void MSG_WriteString (msg_t *sb, const char *s);
 void MSG_WriteBigString (msg_t *sb, const char *s);
 void MSG_WriteAngle16 (msg_t *sb, float f);
+int MSG_HashKey(const char *string, int maxlen);
 
 void	MSG_BeginReading (msg_t *sb);
 void	MSG_BeginReadingOOB(msg_t *sb);
@@ -799,7 +800,6 @@ void 		Com_Quit_f( void );
 int			Com_Milliseconds( void );	// will be journaled properly
 unsigned	Com_BlockChecksum( const void *buffer, int length );
 char		*Com_MD5File(const char *filename, int length, const char *prefix, int prefix_len);
-int			Com_HashKey(char *string, int maxlen);
 int			Com_Filter(char *filter, char *name, int casesensitive);
 int			Com_FilterPath(char *filter, char *name, int casesensitive);
 int			Com_RealTime(qtime_t *qtime);
diff --git a/code/server/sv_client.c b/code/server/sv_client.c
index 4387d24b..1195c88b 100644
--- a/code/server/sv_client.c
+++ b/code/server/sv_client.c
@@ -1605,7 +1605,7 @@ static void SV_UserMove( client_t *cl, msg_t *msg, qboolean delta ) {
 	// also use the message acknowledge
 	key ^= cl->messageAcknowledge;
 	// also use the last acknowledged server command in the key
-	key ^= Com_HashKey(cl->reliableCommands[ cl->reliableAcknowledge & (MAX_RELIABLE_COMMANDS-1) ], 32);
+	key ^= MSG_HashKey(cl->reliableCommands[ cl->reliableAcknowledge & (MAX_RELIABLE_COMMANDS-1) ], 32);
 
 	Com_Memset( &nullcmd, 0, sizeof(nullcmd) );
 	oldcmd = &nullcmd;